Artem Oganov, one of the most cited theoretical mineralogists in the world, told us about a computer prediction that has recently become achievable. Previously, this problem could not be solved because the problem of computer design of new materials includes the problem of crystal structures, which was considered unsolvable. But thanks to the efforts of Oganov and his colleagues, we managed to get closer to this dream and make it a reality.

Why this task is important: In the past, new substances were produced for a very long time and with a lot of effort.

Artem Oganov: “Experimenters are going to the laboratory. Mix different substances at different temperatures and pressures. Get new substances. Measure their properties. As a rule, these substances are of no interest and are discarded. And the experimenters are trying again to get a slightly different substance under different conditions, with a slightly different composition. And so, step by step, we overcome many failures, spending years of our lives on this. It turns out that researchers, in the hope of obtaining one material, spend a huge amount of effort, time, and money. This process may take years. It may turn out to be a dead end and never lead to the discovery of the desired material. But even when it leads to success, that success comes at a very high price."

Therefore, it is necessary to create a technology that could make error-free predictions. That is, not to experiment in laboratories, but to give the computer the task of predicting what material, with what composition and temperature, will have the desired properties under certain conditions. And the computer, sorting through numerous options, will be able to answer which chemical composition and which crystal structure will meet the given requirements. The result may be such that the desired material does not exist. Or he is and not alone.
And here a second problem arises, the solution of which has not yet been solved: how to get this material? That is, the chemical composition, the crystal structure is clear, but there is still no way to implement it, for example, on an industrial scale.

Prediction Technology

The main thing to predict is the crystal structure. Previously, it was not possible to solve this problem, because there are many options for the arrangement of atoms in space. But the vast majority of them are of no interest. What is important are those options for the arrangement of atoms in space that are sufficiently stable and have the properties necessary for the researcher.
What are these properties: high or low hardness, electrical conductivity and thermal conductivity, and so on. The crystal structure is important.

“If you think about, say, carbon, look at diamond and graphite. Chemically, they are the same substance. But the properties are completely different. Black super soft carbon and transparent super hard diamond - what makes the difference between them? It's the crystal structure. It is thanks to her that one substance is superhard, the other is supersoft. One is an almost metal conductor. The other is a dielectric."

In order to learn how to predict a new material, one must first learn how to predict the crystal structure. To do this, Oganov and his colleagues proposed an evolutionary approach in 2006.

“In this approach, we are not trying to try out the whole infinite number of crystal structures. We will try it step by step, starting with a small random sample, within which we rank possible solutions, the worst of which we discard. And from the best we produce child variants. Daughter variants are produced by various mutations or by recombination - by heredity, where from two parents we combine different structural features of the composition. From this, a child structure is obtained - a child material, a child chemical composition, a child structure. These child compounds are then also evaluated. For example, by stability or by the chemical or physical property that interests you. And those that were ranked unfavorable, we discard. Those that are promising get the right to procreate. By mutation or heredity we produce the next generation.”

So, step by step, scientists are approaching the optimal material for them in terms of a given physical property. The evolutionary approach in this case works in the same way as the Darwinian theory of evolution, this principle is carried out by Oganov and his colleagues on a computer when searching for crystal structures that are optimal in terms of a given property or stability.

“I can also say (but this is already a little on the verge of hooliganism) that when we carried out the development of this method (by the way, development is ongoing. It has been improved more and more), we experimented with different ways of evolution. For example, we tried to produce one child not from two parents, but from three or four. It turned out that, just as in life, it is optimal to produce one child from two parents. One child has two parents - father and mother. Not three, not four, not twenty-four. This is the optimum both in nature and on the computer.”

Oganov patented his method, and now it is used by almost thousands of researchers around the world and several major companies such as Intel, Toyota and Fujitsu. Toyota, for example, Oganov said, has been using this method for some time to invent a new material for lithium batteries to be used in hybrid cars.

Diamond problem

It is believed that diamond, being the hardest record holder, is the optimal superhard material for all applications. However, this is not so, because in iron, for example, it dissolves, but in an oxygen environment it burns at a high temperature. In general, the search for a material that would be harder than diamond worried mankind for many decades.

“A simple computer calculation that was carried out by my group shows that such material cannot exist. In fact, only diamond can be harder than diamond, but in nano-crystalline form. Other materials cannot beat diamond in terms of hardness.”

Another direction of Oganov's group is the prediction of new dielectric materials that could serve as the basis for supercapacitors for storing electrical energy, as well as for further miniaturization of computer microprocessors.
“This miniaturization is actually facing obstacles. Because the available dielectric materials can withstand electrical charges quite poorly. They are leaking. And further miniaturization is impossible. If we can get a material that sticks to silicon, but at the same time has a much higher dielectric constant than the materials we have, then we can solve this problem. And we have quite serious progress in this direction as well.”

And the last thing Oganov does is the development of new drugs, that is, their prediction too. This is possible due to the fact that scientists have learned to predict the structure and chemical composition of the surface of crystals.

“The fact is that the surface of a crystal often has a chemical composition that differs from the very substance of the crystal. The structure is also very often radically different. And we found that the surfaces of simple, seemingly inert oxide crystals (such as magnesium oxide) contain very interesting ions (such as the peroxide ion). They also contain groups similar to ozone, consisting of three oxygen atoms. This explains one extremely interesting and important observation. When a person inhales fine particles of oxide minerals, which are seemingly inert, safe and harmless, these particles play a cruel joke and contribute to the development of lung cancer. In particular, asbestos, which is extremely inert, is known to be a carcinogen. So, on the surface of such minerals as asbestos and quartz (especially quartz), peroxide ions can form, which play a key role in the formation and development of cancer. Using our technique, it is also possible to predict the conditions under which the formation of such particles could be avoided. That is, there is hope even to find a therapy and prevention of lung cancer. In this case, we are only talking about lung cancer. And in a completely unexpected way, the results of our research have made it possible to understand, and maybe even prevent or cure lung cancer.”

To sum up, the prediction of crystal structures can play a key role in the design of materials for both microelectronics and pharmaceuticals. In general, such technology opens up a new path in the technology of the future, Oganov is sure.

You can read about other areas of Artem's laboratory at the link, and read his book Modern Methods of Crystal Structure Prediction

1. 1. Computer design of new materials: dream or reality? Artem Oganov (ARO) (1) Department of Geosciences (2) Department of Physics and Astronomy (3) New York Center for Computational Sciences State University of New York, Stony Brook, NY 11794-2100 (4) Moscow State University, Moscow, 119992, Russia.
2. 2. The structure of matter: atoms, molecules The ancients guessed that matter consists of particles: "when He (God) did not create the earth, nor the fields, nor the initial dust particles of the universe" (Proverbs, 8:26) (also - Epicurus, Lucretius Car , ancient Indians, ...) In 1611, I. Kepler suggested that the structure of ice, the form of snowflakes, is determined by their atomic structure
3. 3. The structure of matter: atoms, molecules, crystals 1669 - the birth of crystallography: Nikolai Stenon formulates the first quantitative law of crystallography inside yourself. It gives the mind a certain limited satisfaction, and its details are so varied that it may be called inexhaustible; that is why it lassoes even the best people so tenaciously and for such a long time ”(J.W. Goethe, amateur crystallographer, 1749-1832) Ludwig Boltzmann (1844-1906) is a great Austrian physicist who built all his theories on ideas about atoms. Criticism of atomism led him to commit suicide in 1906. In 1912, the hypothesis of the atomic structure of matter was proved by the experiments of Max von Laue.
4. 4. Structure is the basis for understanding the properties and behavior of materials (from http://nobelprize.org) Zinc blende ZnS. One of the first structures solved by the Braggs In 1913. Surprise: there are NO ZnS molecules in the structure!
5. 5. X-ray diffraction is the main method for experimental determination of the crystal structure Structure Diffraction pattern
6. 6. Correlation between structure and diffraction pattern What will be the diffraction pattern of these "structures"?
7. 7. Triumphs of the experiment - determination of incredibly complex crystalline structures Incommensurate phases Quasicrystals of elements Proteins (Rb-IV, U.Schwarz'99) A new state of matter, discovered in 1982. Found in nature only in 2009! Nobel Prize 2011!
8. 8. States of matter Crystalline Quasicrystalline Amorphous Liquid Gaseous (“Soft matter” – polymers, liquid crystals)
9. 9. Atomic structure is the most important characteristic of matter. Knowing it, one can predict the properties of the material and its electronic structure. Theory Exp. C11 493 482 C22 546 537 C33 470 485 C12 142 144 C13 146 147 C23 160 146 C44 212 204 C55 186 186 Elastic constants of MgSiO3 perovskite C66 149 147
10. 10. A few stories 4. Materials of the earth's interior 3. Materials from a computer 2. Is it possible to predict crystalline1. About the connection of structure? structure and properties
11. 11. Why is ice lighter than water? The structure of ice contains large empty channels, which are not found in liquid water. Due to the presence of these empty channels, ice is lighter than ice.
12. 12. Gas hydrates (clathrates) - ice filled with guest molecules (methane, carbon dioxide, chlorine, xenon, etc.) Number of publications on clathrates Huge deposits of methane hydrate - hope and salvation of energy? Under low pressure, methane and carbon dioxide form clathrates - 1 liter of clathrate contains 168 liters of gas! Methane hydrate looks like ice but burns to release water. Is CO2 hydrate a form of carbon dioxide storage? The mechanism of xenon anesthesia is the formation of Xe-hydrate, which blocks the transmission of neuronal signals to the brain (Pauling, 1951)
13. 13. Microporous materials for the chemical industry and environmental purification Zeolites are microporous aluminosilicates. The separation of octane and iso-octane by zeolite is used in chemical industry. industry Historical examples of heavy metal poisoning: Qin Shi Huangdi Ivan IV the Terrible "Illness of Nero (37-68) Lead (259 - 210 BC) (1530-1584) insane poisoning: hatter" aggression, dementia
14. 14. New and old superconductors The phenomenon was discovered in 1911 by Kamerling-Onnes Theory of superconductivity - 1957 (Bardeen, Cooper, Schrieffer), but there is no theory of the highest temperature superconductors (Bednorz, Muller, 1986)! The most powerful magnets (MRI, mass spectrometers, particle accelerators) Magnetic levitation trains (430 km/h)
15. 15. Surprise: superconducting impurity forms of carbon 1.14 1 Tc  exp[ ] kB g (E F)V Doped graphite: KC8 (Tc=0.125 K), CaC6 (Tc=11 K). B-doped diamond: Tc=4 K. Doped fullerenes: RbCs2C60 (Tc=33 K) Molecule of the molecule Structure and appearance of C60 fullerite fullerene crystals Superconductivity in organic crystals has been known since 1979 (Bechgaard, 1979).
16. 16. How materials can save or destroy At low temperatures, tin undergoes a phase transition - "tin plague". 1812 - according to legend, Napoleon's expedition to Russia died because of tin buttons on his uniforms! 1912 - the death of the expedition of Captain R.F. Scott to the South Pole, which was attributed to the "tin plague". First-order transition at 13 0C White tin: 7.37 g/cm3 Gray tin: 5.77 g/cm3
17. 17. Shape memory alloys 1 2 3 4 1- before deformation 3- after heating (20°C) (50°C) 2- after deformation 4- after cooling (20°C) (20°C) Example: NiTi ( nitinol) Applications: Shunts, dental braces, elements of oil pipelines and aircraft engines
18. 18. Miracles of optical properties Pleochroism (cordierite) - discovery of America and US Air Force navigation Birefringence of light (calcite) Alexandrite effect (chrysoberyl) Lycurgus cup (glass with nanoparticles)
19. 19. About the nature of color Wavelength, Å Color Complementary color 4100 Violet Lemon Yellow 4300 Indigo Yellow 4800 Blue Orange 5000 Blue Green Red 5300 Green Magenta 5600 Lemon Yellow Violet 5800 Yellow Indigo 6100 Orange Blue 6800 Red Blue Green
20. 20. Color depends on direction (pleochroism). Example: cordierite (Mg,Fe)2Al4Si5O18.
21. 21. 2. Prediction of crystal structures Oganov A.R., Lyakhov A.O., Valle M. (2011). How evolutionary crystal structure prediction works - and why. acc. Chem. Res. 44, 227-237.
22. 22. J. Maddox (Nature, 1988) The task is to find the GLOBAL minimum of Natoms Variants Time energy. 1 1 1 sec. It's impossible to enumerate all structures: 10 1011 103 yrs. 20 1025 1017 yrs. 30 1039 1031 yrs. Overview of the USPEX method (ARO & Glass, J.Chem.Phys. 2006)
23. 23. How to use kangaroo evolution to find Mount Everest? (picture by R. Clegg) We land kangaroo troops and let them breed (not shown for censorship reasons).....
24. 24. How to use kangaroo evolution to find Mount Everest? (picture by R. Clegg) Aaaargh! Ouch ....and from time to time hunters come and remove kangaroos at lower altitudes
25. 25.
26. 26. Evolutionary calculations "self-learn" and focus the search on the most interesting regions of space
27. 27. Evolutionary calculations "self-learn" and focus the search on the most interesting regions of space
28. 28. Evolutionary calculations "self-learn" and focus the search on the most interesting regions of space
29. 29. Evolutionary calculations "self-learn" and focus the search on the most interesting regions of space
30. 30. Alternative methods: Random search (Freeman & Catlow, 1992; van Eijck & Kroon, 2000; Pickard & Needs, 2006) No "training", only works for simple systems (up to 10-12 atoms). Artificial annealing (Pannetier 1990 ; Schön & Jansen 1996) No "learning" Metadynamics (Martonak, Laio, Parrinello 2003) Taboo search in reduced space Minima hopping (Gödecker 2004) Uses calculation history and "self learning". Bush (1995), Woodley (1999) genetic and evolutionary algorithms are an inefficient method for crystals. Deaven & Ho (1995) is an efficient method for nanoparticles.
31. 31. USPEX(Universal Structure Predictor: Evolutionary Xtallography) (Random) initial population The new generation of structures is produced only from the best current structures (1) Inheritance (3) Coordinate (2) Lattice mutation mutation (4) Permutation
32. 32. Additional techniques - order parameter "Fingerprint" of the structure Birth of order from chaos in the evolutionary process ["GOD = Generator Of Diversity" © S. Avetisyan] Local order - indicates defective areas
33. 33. Test: “Who would guess that graphite is the stable allotrope of carbon at ordinary pressure?” (Maddox, 1988) Three-dimensional sp2 structure proposed by R. Hoffmann (1983) as a stable phase at 1 atm Structures with low sp3- energy hybridization illustrate sp2 hybridization carbon chemistry sp hybridization (carbine)
34. Test: High pressure phases are also reproduced correctly 100 GPa: diamond stable 2000 GPa: bc8 phase stable + found metastable phase explaining Metastable bc8 phase of silicon "superhard graphite" is known (Kasper, 1964) (Li, ARO, Ma, et al., PRL 2009)
35. 35. Discoveries made with USPEX:
36. 36. 3. Materials from the computer
37. 37. Discovery of New Materials: Still an Experimental Trial and Error "I didn't fail (ten thousand) but only discovered 10,000 ways that didn't work" (T.A. Edison)
38. 38. Search for the densest substance: are modifications of carbon denser than diamond possible? Yes The Structure of DiamondDiamond has the smallest atomic volume and the greatest incompressibility of all the new structure, elements (and compounds). denser than a diamond! (Zhu, ARO, et al., 2011)
39. 39. The analogy of the forms of carbon and silica (SiO2) makes it possible to understand the density of new forms of carbon New structures, 1.1-3.2% denser than diamond, very high (up to 2.8!) refractive indices and light dispersion diamond hP3 structure tP12 structure tI12 structure SiO2 cristobalite SiO2 quartz SiO2 kitite high pressure SiS2 phase
40. 40.
41. 41. The hardest oxide is TiO2? (Dubrovinsky et al., Nature 410, 653-654 (2001)) Nishio-Hamane (2010) and Al-Khatatbeh (2009): compression modulus ~300 GPa instead of 431 GPa. Lyakhov & ARO (2011): Pressure experiments are very difficult! Hardness not higher than 16 GPa! TiO2 is softer than SiO2 of stishovite (33 GPa), B6O (45 GPa), Al2O3 of corundum (21 GPa).
42. 42. Are forms of carbon harder than diamond possible? No . Material Model Li Lyakhov Exp. Hardness, Enthalpy, et al. & ARO Structure GPa eV/atom (2009) (2011) Diamond 89.7 0.000 Diamond 91.2 89.7 90 Lonsdaleite 89.1 0.026 Graphite 57.4 0.17 0.14 C2/m 84.3 0.163 TiO2 rutile 12.4 12.3 8-10 I4 /mmm 84.0 0.198 β-Si3N4 23.4 23.4 21 Cmcm 83.5 0.282SiO2 stishovite 31.8 30.8 33 P2/m 83.4 0.166 I212121 82.9 0.784 Fmmm 82.2 0.322 Cmcm 82.0 0.224 P6522 81.3 0.111 All the hardest structures are based on sp3 -hybridization evolutionary calculation
43. 43. Cold compression of graphite gives M-carbon, not diamond! M-carbon was proposed in 2006. In 2010-2012. Dozens of alternative structures have been proposed (W-, R-, S-, Q-, X-, Y-, Z-carbon, etc.) M-carbon is confirmed by the latest experiments M-carbon is most easily formed from graphite graphite bct4-carbon graphite M - carbon graphite diamond
44. 44. M-carbon - a new form of carbon diamondgraphite lonsdaleite Theoretical phase diagram of carbon M-carbonfullerenes carbines
45. 45. Substance under pressure in nature P.W. Bridgman 1946 Nobel Laureate (Physics) 200x Scale: 100 GPa = 1 Mbar =
46. Neptune has an internal heat source - but where does CH4 come from? Uranus and Neptune: H2O:CH4:NH3 = 59:33:8. Neptune has an internal energy source (Hubbard'99). Ross'81 (and Benedetti'99): CH4=C(diamond) + 2H2. Is falling diamond the main source of heat on Neptune? The theory (Ancilotto’97; Gao’2010) confirms this. methane hydrocarbons diamond
47. 47. Boron is located between metals and non-metals and its unique structures are sensitive to B impurities, temperature and pressure alpha-B beta-B T-192
48. 48. The history of the discovery and research of boron is full of contradictions and detective turns B 1808: J.L. Gay-Lussac and H. Davy announced the discovery of a new element - boron. J.L. Gay-Lussac H. Davy 1895: H. Moissan proved that the substances they discovered contained no more than 50-60% boron. The Moissan material, however, also turned out to be a compound with a boron content of less than 90%. H. Moissan 1858: F. Wöhler described 3 modifications of boron - "diamond-", "graphite-" and "coal-like". All three turned out to be compounds (for example, AlB12 and B48C2Al). 2007: ~16 crystal modifications have been published (most are compounds?). It is not known which form is the most stable. F. Wöhler
49. 49. Under pressure, boron forms a partially ionic structure! B 2004: Chen and Solozhenko: synthesized a new modification of boron, but could not solve its structure. 2006: Oganov: determined the structure, proved its stability. 2008: Solozhenko, Kurakevich, Oganov - this phase is one of the hardest known substances (hardness 50 GPa). X-ray diffraction. Top - theory, Bottom - experiment Structure of gamma-boron: (B2)δ+(B12)δ-, δ=+0.5 (ARO et al., Nature 2009). Distribution of the most (left) and least (right) stable electrons.
50. 50. The first phase diagram of boron - after 200 years of research! Boron phase diagram (ARO et al., Nature 2009)
51. 51. Sodium is a metal perfectly described by the free electron model
52. 52. Under pressure, sodium changes its essence - "alchemical transformation" Na 1807: Sodium discovered by Humphrey Davy. 2002: Hanfland, Syassen, et al. - the first indication of extremely complex chemistry H. Davy sodium pressure over 1 Mbar. Gregoryants (2008) for more detailed data. Under pressure, sodium becomes partly a d-metal!
53. 53. We have predicted a new structure, which is a transparent non-metal! Sodium becomes transparent at a pressure of ~2 Mbar (Ma, Eremets, ARO et al., Nature 2009) Electrons are localized in the "empty space" of the structure, which makes compressed sodium a non-metal
54. The study of minerals is not only an aesthetic pleasure, but also a practically and fundamentally important scientific direction Effect of lowering the melting point by impurities Wood's alloy - melts at 70 C. Bi-Pb-Sn-Cd-In-Tl alloy - at 41.5 C!
55. 64. And what is the composition of the inner core of the Earth? The core is somewhat less dense than pure iron. In the Fe core in an alloy with light elements such as S, Si, O, C, H. New compounds (FeH4!) are predicted in the Fe-C and Fe-H systems. Carbon can be contained in the nucleus in large quantities [Bazhanova, Oganov, Dzhanola, UFN 2012]. Percentage of carbon in the inner core needed to explain its density
56. 65. The nature of layer D” (2700-2890 km) remained a mystery for a long time D” – the root of hot mantle flows MgSiO3 is expected to be ~75 vol.% Strangeness of layer D”: seismic discontinuity, anisotropy Recall the anisotropy of cordierite color!
57. 66. The answer lies in the existence of a new mineral, MgSiO3 post-perovskite in layer D“ (2700-2890 km) Perovskite as the Earth cools D“ absent from Mercury and Mars New family of minerals predicted Confirmation – Tschauner (2008)
58. 67. The structure of matter is the key to understanding the world 4. The understanding of the planetary interior is deepening 3. The computer learns to predict new materials 2. It is already possible to predict crystal structures1. Structure defines properties
59. 68. Acknowledgments: My students, graduate students and postdocs: A. Lyakhov Y. Ma S.E. Boulfelfel C.W. Glass Q. Zhu Y. Xie Colleagues from other laboratories: F. Zhang (Perth, Australia) C. Gatti (U. Milano, Italy) G. Gao (Jilin University, China) A. Bergara (U. Basque Country, Spain) I. Errea (U. Basque Country, Spain) M. Martinez-Canales (UCL, U.K.) C. Hu (Guilin, China) M. Salvado & P.Pertierra (Oviedo, Spain) V.L. Solozhenko (Paris) D.Yu. Pushcharovsky, V.V. Brazhkin (Moscow) Users of the USPEX program (>1000 people) - http://han.ess.sunysb.edu/~USPEX

We publish the text of a lecture delivered by a professor at the State University of New York, an associate professor at Moscow State University, an honorary professor at Guilin UniversityArtem Oganov 8 September 2012 as part of the Polit.ru public lecture series at the open-air book festival BookMarket in the park of arts "Museon".

"Public lectures "Polit.ru"" are held with the support of:

Lecture text

I am very grateful to the organizers of this festival and Polit.ru for the invitation. It is a great honor for me to give this lecture; I hope it will be of interest to you.

The lecture is directly related to our future, because our future is impossible without new technologies, technologies related to our quality of life, here is the iPad, here is our projector, all our electronics, energy-saving technologies, technologies that are used to clean the environment, technologies that used in medicine and so on - all this depends to a large extent on new materials, new technologies require new materials, materials with unique, special properties. And about how these new materials can be developed not in the laboratory, but on a computer, the story will go.

The lecture is called: "Computer design of new materials: dream or reality?". If it were just a dream, then the lecture would have no meaning. Dreams are something, as a rule, not from the realm of reality. On the other hand, if this had already been fully realized, the lecture would also have no meaning, because a new kind of methodologies, including theoretical computational ones, when they are already fully developed, move from the category of science to the category of industrial routine tasks. In fact, this field is completely new: the computer design of new materials is somewhere in the middle between a dream - something that is impossible, something that we dream about at our leisure - and reality, it is not yet fully completed area, it is an area that being developed right now. And this area will allow in the near future to retreat from the traditional method of discovering new materials, laboratory, and start computer-aided design of materials, which would be both cheaper and faster, and in many respects even more reliable. And here's how to do it, I'll tell you. This is directly related to the problem of prediction, the prediction of the structure of a substance, because the structure of a substance determines its properties. The different structure of the same substance, say, carbon, defines superhard diamond and supersoft graphite. Structure in this case is everything. The structure of matter.

In general, this year we are celebrating the centenary of the first experiments that made it possible to discover the structure of matter. A very long time ago, since ancient times, people put forward hypotheses that matter consists of atoms. A mention of this can be found, for example, in the Bible, in various Indian epics, and quite detailed references to this can be seen in Democritus and Lucretius Kara. And the first mention of how matter is arranged, how this substance consists of these discrete particles, atoms, belongs to Johannes Kepler, the great mathematician, astronomer and even astrologer - at that time astrology was still considered a science, unfortunately. Kepler drew the first pictures in which he explained the hexagonal shape of snowflakes, and the structure of ice proposed by Kepler, although different from reality, is similar in many respects. But, nevertheless, the hypothesis of the atomic structure of matter remained a hypothesis until the 20th century, until a hundred years ago for the first time this hypothesis became scientifically proven. It became proven with the help of my science, crystallography, a relatively new science, which was born in the middle of the 17th century, 1669 is the official birth date of the science of crystallography, and it was created by the wonderful Danish scientist Nikolai Stenon. Actually, his name was Nils Stensen, he was a Dane, the Latinized name is Nikolai Stenon. He founded not only crystallography, but a number of scientific disciplines, and he formulated the first law of crystallography. Since that time, crystallography along an accelerating trajectory began to develop.

Nicholas Stenon had a unique biography. He became not only the founder of several sciences, but was also canonized in the Catholic Church. The greatest German poet Goethe was also a crystallographer. And Goethe quotes that crystallography is unproductive, exists within itself, and in general this science is completely useless, and it is not clear why it is needed, but like a puzzle it is very interesting, and due to this it attracts very smart people. This is what Goethe said in a popular science lecture he gave somewhere in the Baden spas to wealthy idle ladies. By the way, there is a mineral named after Goethe, goethite. It must be said that at that time crystallography was really a rather useless science, really at the level of some kind of mathematical charades and puzzles. But time passed, and 100 years ago crystallography left the category of such sciences in itself and became an exceptionally useful science. This was preceded by a great tragedy.

Again, the atomic structure of matter remained a hypothesis until 1912. The great Austrian physicist Ludwig Boltzmann built all his scientific arguments on this hypothesis about the atomicity of matter and was severely criticized by many of his opponents: “how can you build all your theories on an unproven hypothesis?” Ludwig Boltzmann, influenced by this criticism, as well as poor health, committed suicide in 1906. He hanged himself while on holiday with his family in Italy. Just 6 years later, the atomic structure of matter was proven. So if he had been a little more patient, he would have triumphed over all his opponents. Patience sometimes means more than intelligence, patience means more than even genius. So - what were these experiments? These experiments were made by Max von Laue, more precisely, by his graduate students. Max von Laue did not do any of these experiments himself, but the idea was his. The idea was that if matter really is made up of atoms, if indeed, as Kepler suggested, atoms are built in a crystal in a periodic regular way, then an interesting phenomenon should be observed. Shortly before that, X-rays were discovered. Physicists by that time already well understood that if the wavelength of the radiation is comparable to the length of the periodicity - the characteristic length of the object, in this case - the crystal, then the phenomenon of diffraction should be observed. That is, the rays will travel not only strictly in a straight line, but also deviate to absolutely strictly defined angles. Thus, some very special X-ray diffraction pattern should be observed from the crystal. It was known that the wavelength of X-rays should be similar to the size of atoms, if atoms exist, estimates of the size of atoms were made. Thus, if the atomic hypothesis of the structure of matter is correct, then X-ray diffraction of crystals should be observed. What could be easier than checking?

A simple idea, a simple experiment, for which in a little more than a year, Laue received the Nobel Prize in Physics. And we can try this experiment. But, unfortunately, it is now too light for everyone to observe this experiment. But maybe we can try it with one witness? Who could come up here and try to observe this experiment?

See. Here is a laser pointer, we shine it - and what is happening here? We don't have x-rays, we have an optical laser. And this is not the structure of the crystal, but its image, swollen 10 thousand times: but the laser wavelength is 10 thousand times greater than the wavelength of X-rays, and thus the diffraction condition is again fulfilled - the wavelength is comparable with the period of the crystal lattice. Let's look at an object in which there is no regular structure, a liquid. Here, Oleg, hold this picture, and I will shine with a laser, come closer, the picture will be small, because we cannot project ... look, you see a ring here, inside there is a point that characterizes the direct passage of the beam. But the ringlet is diffraction from the unorganized structure of the liquid. If we have a crystal in front of us, then the picture will be completely different. You see, we have a lot of rays that deviate at strictly defined angles.

Oleg (volunteer): Probably because there are more atoms...

Artyom Oganov: No, due to the fact that the atoms are arranged in a strictly defined way, we can observe such a diffraction pattern. This picture is very symmetrical, and this is important. Let's applaud Oleg for a brilliantly conducted experiment that would have brought him a Nobel Prize 100 years ago.

Then, the following year, Braggy's father and son learned to decipher diffraction patterns and identify crystal structures from them. The first structures were very simple, but now, thanks to the latest methodologies, for which the Nobel Prize was awarded in 1985, it is possible to decipher already very, very complex structures, based on experiment. Here is the experiment that Oleg and I reproduced. Here is the original structure, here are benzene molecules, and Oleg observed such a diffraction picture. Now, with the help of experiment, it is possible to decipher very complex structures, in particular the structures of quasicrystals, and last year the Nobel Prize in Chemistry was given for the discovery of quasicrystals, this new state of solid matter. How dynamic this area is, what fundamental discoveries are being made in our lifetime! The structure of proteins and other biologically active molecules is also deciphered by X-ray diffraction, that great crystallographic technique.

So, we know the different states of matter: ordered crystalline and quasi-crystalline, amorphous (disordered solid state), as well as liquid, gaseous state and various polymeric states of matter. Knowing the structure of matter, you can predict many, many of its properties, and with a high degree of reliability. Here is the structure of magnesium silicate, a type of perovskite. Knowing the approximate positions of atoms, you can predict, for example, such a rather difficult property as elastic constants - this property is described by a rank 4 tensor with many components, and you can predict this complex property with experimental accuracy, knowing only the position of atoms. And the substance is quite important, it makes up 40% of the volume of our planet. It is the most common material on earth. And to understand the properties of this substance, which exists at great depths, it is possible, knowing only the arrangement of atoms.

I would like to talk a little about how properties are related to structure, how to predict the structure of matter in order to be able to predict new materials, and what has been done using these kinds of methods. Why is ice lighter than water? We all know that icebergs float and don't sink, we know that ice is always on the surface of the river, not at the bottom. What's the matter? It's about structure: if you look at this structure of ice, you will see large hexagonal voids in it, and when the ice starts to melt, water molecules clog these hexagonal voids, due to which the density of water becomes greater than the density of ice. And we can demonstrate how this process happens. I will show you a short film, watch carefully. The melting will start from the surfaces, that's how it actually happens, but this is a computer calculation. And you will see how the melting spreads inward ... the molecules move, and you see how these hexagonal channels become clogged, and the correctness of the structure is lost.

Ice has several different forms, and the form of ice that is obtained by filling the voids of the ice structure with guest molecules is very interesting. But the structure itself will also change. I am talking about the so-called gas hydrates or clathrates. You see a framework of water molecules, in which there are voids, in which there are guest molecules or atoms. Guest molecules can be methane - natural gas, can be carbon dioxide, can be, for example, a xenon atom, and each of these gas hydrates has an interesting history. The fact is that methane hydrate reserves contain 2 orders of magnitude more natural gas than conventional gas fields. Deposits of this type are located, as a rule, on the sea shelf and in permafrost zones. The problem is that people still have not learned how to safely and cost-effectively extract gas from them. If this problem is solved, then humanity will be able to forget about the energy crisis, we will have an almost inexhaustible source of energy for the coming centuries. Carbon dioxide hydrate is very interesting - it can be used as a safe way to bury excess carbon dioxide. You pump carbon dioxide under slight pressure into the ice and dump it on the seafloor. This ice has existed there quite calmly for many thousands of years. Xenon hydrate was the explanation for xenon anesthesia, a hypothesis that was put forward 60 years ago by the great crystal chemist Linus Pauling: the fact is that if a person is allowed to breathe xenon under slight pressure, the person stops feeling pain. It has been and seems to be sometimes used as an anesthetic for surgical procedures. Why?

Xenon under slight pressure forms compounds with water molecules, forming the very gas hydrates that clog the propagation of an electrical signal through the human nervous system. And the pain signal from the operated tissue simply does not reach the muscles, due to the fact that xenon hydrate is formed with just such a structure. This was the very first hypothesis, perhaps the truth is a little more complicated, but there is no doubt that the truth is nearby. When we talk about such porous substances, we cannot help but recall microporous silicates, the so-called zeolites, which are very widely used in industry for catalysis, as well as for separating molecules during oil cracking. For example, octane and mesooctane molecules are perfectly separated by zeolites: this is the same chemical formula, but the structure of the molecules is slightly different: one of them is long and thin, the other is short and thick. And the one that is thin passes through the voids of the structure, and the one that is thick is sifted out, and therefore such structures, such substances are called molecular sieves. These molecular sieves are used to purify water, in particular, the water that we drink in our taps, it must pass through multiple filtrations, including with the help of zeolites. You can thus get rid of pollution with a variety of chemical pollutants. Chemical contaminants are sometimes extremely dangerous. History knows examples of how heavy metal poisoning led to very sad historical examples.

Apparently, the first emperors of China, Qin Shi Huangdi, and Ivan the Terrible, were victims of mercury poisoning, and the so-called mad hatter's disease was very well studied, in the 18-19 centuries in England a whole class of people working in the hat industry fell ill very early with a strange a neurological disease called the mad hatter's disease. Their speech became incoherent, their actions meaningless, their limbs trembled uncontrollably, and they fell into dementia and madness. Their body was in constant contact with mercury, as they soaked these hats in solutions of mercury salts, which entered their body and affected the nervous system. Ivan the Terrible was a very progressive, good tsar under the age of 30, after which he changed overnight - and became an insane tyrant. When his body was exhumed, it turned out that his bones were sharply deformed, and they contained a huge concentration of mercury. The fact is that the tsar suffered from a severe form of arthritis, and at that time arthritis was treated by rubbing mercury ointments - this was the only remedy, and perhaps just mercury explains the strange madness of Ivan the Terrible. Qin Shi Huang, the man who created China in its current form, ruled for 36 years, and for the first 12 years he was a puppet in the hands of his mother, the regent, his story is similar to the story of Hamlet. His mother and lover killed his father, and then they tried to get rid of him too, a terrible story. But, having matured, he began to rule himself - and in 12 years he stopped the internecine war between the 7 kingdoms of China, which lasted 400 years, united China, he united weights, money, unified Chinese writing, he built the Great Wall of China, he built 6 5,000 kilometers of highways that are still in use, canals that are still in use, and it was all done by one man, but in recent years he has suffered some strange form of manic insanity. His alchemists, in order to make him immortal, gave him mercury pills, they believed that this would make him immortal, as a result, this man, apparently distinguished by remarkable health, died before reaching 50 years old, and the last years of this short life were clouded by madness. Lead poisoning may have made many Roman emperors its victims: in Rome there was a lead plumbing, an aqueduct, and it is known that with lead poisoning, certain parts of the brain shrink, you can even see this on tomographic pictures, intelligence drops, IQ drops, a person becomes very aggressive . Lead poisoning is still a big problem for many cities and countries. To get rid of this kind of undesirable consequences, we need to develop new materials to clean up the environment.

Interesting materials, not fully explained, are superconductors. Superconductivity was also discovered 100 years ago. This phenomenon is largely exotic, it was discovered in a random way. They simply cooled mercury in liquid helium, measured the electrical resistance, it turned out that it drops exactly to zero, and later it turned out that superconductors completely push out the magnetic field and are able to levitate in a magnetic field. These two characteristics of superconductors are widely used in high-tech applications. The type of superconductivity that was discovered 100 years ago was explained, it took half a century to explain, this explanation brought the Nobel Prize to John Bardeen and his colleagues. But then in the 80s, already in our century, a new type of superconductivity was discovered, and the best superconductors belong precisely to this class - high-temperature superconductors based on copper. An interesting feature is that such superconductivity still has no explanation. There are many applications for superconductors. For example, with the help of superconductors, the most powerful magnetic fields are created, and this is used in magnetic resonance imaging. Maglev levitating trains are another use, and here's a photo I personally took in Shanghai on a maglev train showing a speed indicator of 431 kilometers per hour. Superconductors are sometimes very exotic: organic superconductors have been known for more than 30 years, that is, superconductors based on carbon, it turns out that even diamond can be made a superconductor by introducing a small amount of boron atoms into it. Graphite can also be made a superconductor.

Here is also an interesting historical parallel about how the properties of materials or their ignorance can have fatal consequences. Two stories that are very beautiful, but apparently not historically correct, but I will tell them anyway, because a beautiful story is sometimes better than a true story. In popular science literature, one can actually often find references to how the effect of the tin plague - and here is its example - ruined the expeditions of Napoleon in Russia and Captain Scott to the South Pole. The fact is that tin at a temperature of 13 degrees Celsius undergoes a transition from metal (this is white tin) to gray tin, a semiconductor, while the density drops sharply - and the tin falls apart. This is called "tin plague" - tin simply crumbles into dust. And here is a story that I have not seen a full explanation. Napoleon comes to Russia with an army of 620 thousand, gives only a few relatively small battles - and only 150 thousand people reach Borodino. 620 come, 150 thousand reach Borodin almost without a fight. Under Borodino, about 40 thousand more victims, then a retreat from Moscow - and 5 thousand reach Paris alive. By the way, the retreat was also almost without a fight. What is going on? How to slide from 620 thousand without a fight to 5 thousand? There are historians who claim that the tin plague is to blame for everything: the buttons on the uniforms of the soldiers were made of tin, the tin crumbled as soon as the cold set in, and the soldiers were actually naked in the Russian frost. The problem is that the buttons were made from dirty tin, which is resistant to tin plague.

Very often you can see in the popular science press a mention that, according to different versions, Captain Scott either carried with him airplanes in which the fuel tanks had tin solders, or canned food in tin cans - the tin again crumbled, and the expedition died of starvation and cold. I actually read the diaries of Captain Scott - he did not mention any airplanes, he had some kind of snowmobile, but again he does not write about the fuel tank, and he does not write about canned food either. So these hypotheses, apparently, are incorrect, but very interesting and instructive. And remembering the effect of the tin plague is at least useful if you are going to a cold climate.

Here is another experiment, and here I need boiling water. Another effect related to materials and their structure, which would not have occurred to any person, is the shape memory effect, also discovered quite by accident. In this illustration, you can see that my colleagues made two letters from this wire: T U, Technical University, they hardened this shape at high temperatures. If you harden some shape at high temperature, the material will remember this shape. You can make a heart, for example, give it to your beloved and say: this heart will remember my feelings forever ... then this shape can be destroyed, but as soon as you put it in hot water, the shape is restored, it looks like magic. You have just broken this form, but you put it in hot water - the form is restored. And all this happens due to a very interesting and rather subtle structural transformation that occurs in this material at a temperature of 60 degrees Celsius, which is why hot water is needed in our experiment. And the same transformation occurs in steel, but in steel it occurs too slowly - and the shape memory effect does not occur. Imagine if steel also showed such an effect, we would live in a completely different world. The shape memory effect has many applications: dental braces, heart bypasses, engine parts in aircraft to reduce noise, soldering in gas and oil pipelines. And now I need another volunteer... please, what's your name? Vika? We need Vicki's help with this wire, it's a shape memory wire. The same alloy nitinol, an alloy of nickel and titanium. This wire was tempered in the form of a straight wire, and he will remember this form forever. Vika, take a piece of this wire and twist it in every possible way, make it as indirect as possible, just don't tie the knots: the knot won't unravel. And now dip it in boiling water, and the wire will remember this shape ... well, straightened out? This effect can be observed forever, I have probably seen it a thousand times, but every time, like a child, I look and admire what a beautiful effect. Let's applaud Vika. It would be great if we could also predict such materials on a computer.

And here are the optical properties of materials, which are also completely non-trivial. It turns out that many materials, almost all crystals, split a beam of light into two beams that travel in different directions and at different speeds. As a result, if you look through the crystal at some inscription, the inscription will always be slightly doubled. But, as a rule, it is indistinguishable for our eyes. In some crystals, this effect is so strong that you can actually see two inscriptions.

Question from the floor: Did you say - at different speeds?

Artem Oganov: Yes, the speed of light is only constant in a vacuum. In condensed media it is lower. Further, we used to think that each material has a certain color. Ruby is red, sapphire is blue, but it turns out that the color can also depend on the direction. In general, one of the main characteristics of a crystal is anisotropy - the dependence of properties on direction. Properties in this direction and in this direction are different. Here is the mineral cordierite, in which the color changes from brownish-yellow to blue in different directions, this is the same crystal. Does anyone believe me? I brought a special crystal of cordierite, so please... look, what color is it?

Question from the floor: Looks white, but...

Artem Oganov: From something light, like white, to purple, you just spin the crystal. In fact, there is an Icelandic legend about how the Vikings discovered America. And many historians see this legend as an indication of the use of this effect. When the Vikings were lost in the middle of the Atlantic Ocean, their king took out a certain sun stone, and in the twilight light managed to determine the direction to the West, and so they sailed to America. Nobody knows what a sun stone is, but many historians believe that a sun stone is what Vika holds in her hands, cordierite, by the way, cordierite is found off the coast of Norway, and with the help of this crystal you can really navigate in twilight, in evening light, as well as in polar latitudes. And this effect was used by the US Air Force until the 50s, when it was replaced by more advanced methods. And here is another interesting effect - alexandrite, if anyone has a desire, I brought a crystal of synthetic alexandrite, and its color changes depending on the light source: in daylight and electric. And, finally, there is another interesting effect that scientists and art critics could not understand for many centuries. The Lycurgus Cup is an object that was made by Roman artisans over 2,000 years ago. In scattered light, this cup is green, and in transmitted light, it is red. And I managed to understand this just a few years ago. It turned out that the bowl is not made of pure glass, but contains gold nanoparticles, which create this effect. Now we understand the nature of color - color is associated with certain absorption ranges, with the electronic structure of matter, and this, in turn, is associated with the atomic structure of matter.

Question from the floor: The concepts of "reflected" and "passing" can be explained?

Artem Oganov: Can! By the way, I note that these very absorption spectra determine why cordierite has a different color in different directions. The fact is that the very structure of the crystal - in particular, cordierite - looks different in different directions, and light is absorbed differently in these directions.

What is white light? This is the entire spectrum from red to violet, and as light passes through the crystal, some of that range is absorbed. For example, a crystal can absorb blue color, and you can see what will be the result from this table. If you absorb blue rays, then the output will be orange, that is, when you see something orange, you know that this substance absorbs in the blue range. Diffused light is when you have the same Lycurgus cup on the table, light falls, and part of this light is scattered and enters your eyes. The scattering of light obeys completely different laws and, in particular, depends on the graininess of the object. Due to the scattering of light, the sky is blue. There is a Rayleigh scattering law that can be used to explain these colors.

I showed you how properties are related to structure. And how it is possible to predict the crystal structure, we will consider briefly now. This means that the problem of predicting crystal structures until very recently was considered unsolvable. This problem itself is formulated as follows: how to find the arrangement of atoms that gives maximum stability - that is, the least energy? How to do it? You can, of course, sort out all the options for the arrangement of atoms in space, but it turns out that there are so many such options that you won’t have enough life to sort through them, in fact, even for fairly simple systems, say, with 20 atoms, you will need more than time the life of the universe to go through all these possible combinations on the computer. Therefore, it was considered that this problem was unsolvable. Nevertheless, this problem was solved, and by several methods, and the most effective method, although it may sound immodest, was developed by my group. The method is called "Success", "USPEX", an evolutionary method, an evolutionary algorithm, the essence of which I will try to explain to you now. The task is equivalent to finding the global maximum on some multidimensional surface - for simplicity, consider a two-dimensional surface, the surface of the Earth, where you need to find the highest mountain without having maps. Let's put it the way my Australian colleague Richard Clegg put it - he's Australian, he loves kangaroos, and in his formulation with the help of kangaroos, rather unintelligent animals, you need to determine the highest point on the surface of the Earth. Kangaroo understands only simple instructions - go up, go down. In the evolutionary algorithm, we drop a kangaroo landing, randomly, to different points on the planet and give each of them an instruction: go up to the top of the nearest hill. And they go. When these kangaroos reach the Sparrow Hills, for example, and when they reach maybe Elbrus, those of them who did not get high are eliminated, shot back. A hunter comes, I almost said, an artist, a hunter comes and shoots, and those who survived get the right to breed. And thanks to this, it is possible to single out the most promising areas from the entire search space. And step by step, by shooting taller and taller kangaroos, you will move the kangaroo population to a global maximum. Kangaroos will produce more and more successful offspring, hunters will shoot higher and higher climbing kangaroos, and thus this population can simply be driven to Everest.

And this is the essence of evolutionary methods. For simplicity, I omit the technical details of exactly how this was implemented. And here is another two-dimensional implementation of this method, here is the energy surface, we need to find the bluest point, here are our initial, random, structures - these are the bold points. The calculation immediately understands which of them are bad, here - in the red and yellow areas, which of them are the most promising: in the blue, greenish areas. And step by step, the sampling density of the most promising areas increases until we find the most adapted, most stable structure. There are different methods for predicting structures - random search methods, artificial annealing, and so on, but the most powerful method turned out to be this evolutionary one.

The most difficult thing is how to produce descendants from parents on a computer. How to take two parent structures and make a child out of them? In fact, on a computer, you can make children not only from two parents, we experimented, we from three, and from four we tried to do it. But, as it turns out, this does not lead to anything good, just like in life. A child is better if there are two parents. By the way, one parent also works, two parents are optimal, and three or four do not work anymore. The evolutionary method has several interesting features, which, by the way, have in common with biological evolution. We see how, from unadapted, random structures with which we start the calculation, highly organized, highly ordered solutions appear in the course of the calculation. We see that the calculations are most effective when the population of structures is the most diverse. The most stable and most surviving populations are the populations of diversity. Here, for example, what I like about Russia is the fact that there are more than 150 nations in Russia. There are fair-haired, there are dark-haired, there are all sorts of people of Caucasian nationality like me, and all this gives the Russian population stability and future. Monotonous populations have no future. This can be seen very clearly from the evolutionary calculations.

Can we predict that the stable form of carbon at atmospheric pressures is graphite? Yes. This calculation is very fast. But in addition to graphite, we produce several interesting, slightly less stable solutions in the same calculation. And these solutions can also be interesting. If we increase the pressure, the graphite is already unstable. A diamond is stable, and we also find it very easily. See how the calculation quickly produces a diamond from disordered initial structures. But before a diamond is found, a number of interesting structures are produced. For example, here is this structure. While the diamond has hexagonal rings, 5 and 7-angle rings are visible here. This structure is only slightly less stable than diamond, and at first we thought it was a curiosity, and then it turned out that this is a new, really existing form of carbon, which was established quite recently by us and our colleagues. This calculation was made at 1 million atmospheres. If we increase the pressure to 20 million atmospheres, the diamond will cease to be stable. And instead of diamond, a very strange structure will be stable, the stability of which for carbon at such pressures has been suspected for many decades, and our calculation confirms this.

A lot has been done by us and our colleagues with the help of this method, here is a small selection of different discoveries. Let me just talk about some of them.

Using this method, it is possible to replace the laboratory discovery of materials with a computer one. In the laboratory discovery of materials, Edison was the unsurpassed champion, saying: "I did not suffer 10 thousand failures, I only found 10 thousand ways that do not work." This tells you how many attempts, unsuccessful attempts to make before making a real discovery with this method, and with the help of computer design, you can achieve success in 1 attempt out of 1, 100 out of 100, 10 thousand out of 10 thousand, this is our the goal is to replace the Edison method with something much more productive.

We can now optimize not only energy, but any property. The simplest property is density, and the densest material known so far is diamond. Diamond is generally a record holder in many respects. There are more atoms in a cubic centimeter of diamond than in a cubic centimeter of any other substance. Diamond holds the record for hardness and is also the least compressible substance known. Can these records be broken? Now we can ask this question to the computer, and the computer will answer. And the answer is yes, some of these records can be broken. It turned out that it is quite easy to beat diamond in terms of density, there are denser forms of carbon that have the right to exist, but have not yet been synthesized. These forms of carbon beat diamond not only in density but also in optical properties. They will have higher refractive indices and light dispersion - what does that mean? The refractive index of a diamond gives the diamond its unsurpassed brilliance and internal reflection of light - and the dispersion of light means that white light will split into a spectrum from red to violet even more than a diamond does. Here, by the way, is the material that often replaces diamond in the jewelry industry - cubic zirconia, cubic zirconia. It surpasses diamond in light dispersion, but, unfortunately, is inferior to diamond in brilliance. And new forms of carbon will beat diamond on both counts. What about hardness? Until 2003, it was believed that hardness is a property that people will never learn to predict and calculate, in 2003 everything changed with the work of Chinese scientists, and this summer I visited Yangshan University in China, where I received another honorary professorship, and there I visited the founder of this whole theory. We have developed this theory.

Here is a table that shows how the calculated hardness definitions agree with experiment. For most normal substances, the agreement is excellent, but for graphite, the models predicted that it should be superhard, which is obviously wrong. We managed to understand and fix this error. And now, with this model, we can reliably predict hardness for any substance, and we can ask the computer the following question: what is the hardest substance? Is it possible to surpass diamond in hardness? People have actually been thinking about this for many, many decades. So, what is the hardest structure carbon has? The answer was discouraging: diamond, and there can be nothing harder in carbon. But you can find structures of carbon that will be close to diamond in hardness. Carbon structures that are close to diamond in hardness really have a right to exist. And one of them is the one I showed you earlier, with 5 and 7 member channels. Dubrovinsky in 2001 proposed in the literature an ultra-hard substance - titanium dioxide, it was believed that it was not much inferior to diamond in hardness, but there were doubts. The experiment was quite controversial. Almost all experimental measurements from that work were refuted sooner or later: it was very difficult to measure the hardness, due to the small size of the samples. But the calculation showed that the hardness was also erroneously measured in that experiment, and the real hardness of titanium dioxide is about 3 times less than what the experimenters claimed. So with the help of this kind of calculations, one can even judge which experiment is reliable and which is not, so these calculations have now reached a high accuracy.

There is another story related to carbon that I would like to tell you - it has been especially violent in the last 6 years. But it began 50 years ago, when American researchers conducted such an experiment: they took graphite and compressed it to a pressure of about 150-200 thousand atmospheres. If graphite is compressed at high temperatures, it must change into diamond, the most stable form of carbon at high pressures, which is how diamond is synthesized. If you do this experiment at room temperature, then the diamond cannot be formed. Why? Because the restructuring that is required to transform graphite into diamond is too great, these structures are too dissimilar, and the energy barrier to be overcome is too great. And instead of the formation of a diamond, we will observe the formation of some other structure, not the most stable, but the one with the lowest formation barrier. We proposed such a structure - and called it M-carbon, this is the same structure with 5- and 7-membered rings; my Armenian friends jokingly call it "mcarbon-shmugler". It turned out that this structure fully describes the results of that experiment 50 years ago, and the experience was repeated many times. The experiment, by the way, is very beautiful - by compressing graphite (a black, soft opaque semi-metal) at room temperature, under pressure, the researchers obtained a transparent superhard non-metal: an absolutely fantastic transformation! But this is not a diamond, its properties do not agree with diamond, and our then hypothetical structure fully described the properties of this substance. We were overjoyed, wrote an article and published it in the prestigious journal Physical Review Letters, and rested on our laurels for exactly one year. A year later, American and Japanese scientists found a new structure, completely different from it, this one, with 4- and 8-membered rings. This structure is completely different from ours, but describes the experimental data almost as well. The problem is that the experimental data was of low resolution, and many other structures were suitable for them. Another six months passed, a Chinese named Wang proposed W-carbon, and W-carbon also explained the experimental data. Soon the story became grotesque - new Chinese bands joined in, and the Chinese love to produce, and they stamped about 40 structures, and they all fit the experimental data: P-, Q-, R-, S-carbon, Q-carbon, X -, Y-, Z-carbon, M10-carbon is known, X'-carbon, and so on - even the alphabet is not enough. So who's right? Generally speaking, our M-carbon initially had exactly the same right to claim to be right as everyone else.

Reply from the audience: Everyone is right.

Artem Oganov: This doesn't happen either! The fact is that nature always chooses extreme solutions. Not only people are extremists, but nature is also an extremist. At high temperatures, nature chooses the most stable state, because at high temperatures you can go through any energy barrier, and at low temperatures, nature chooses the smallest barrier, and there can be only one winner. There can only be one champion - but who exactly? You can do a high resolution experiment, but people have been trying for 50 years and no one succeeded, all the results were of poor quality. You can do the calculation. And in the calculation it would be possible to consider the activation barriers to the formation of all these 40 structures. But, firstly, the Chinese are still churning out new and new structures, and no matter how hard you try, there will still be some Chinese who will say: I have one more structure, and you will count these for the rest of your life. activation barriers until you are sent to a well-deserved rest. This is the first difficulty. The second difficulty is that it is very, very difficult to count activation barriers in solid-state transformations, this is an extremely non-trivial task, special methods and powerful computers are needed. The fact is that these transformations do not occur in the entire crystal, but first in a small fragment - the embryo, and then it spreads to the nucleus and further. And modeling this embryo is an extremely difficult task. But we found such a method, a method that was developed earlier by Austrian and American scientists, and adapted it to our task. We managed to modify this method in such a way that with one blow we were able to solve this problem once and for all. We posed the problem as follows: if you start with graphite, a hard-coded initial state, and the final state is given vaguely - any tetrahedral, sp3-hybridized form of carbon (and these are the states we expect under pressure), then which of the barriers will be minimal? This method can count barriers and finds the minimum barrier, but if we set the final state as an ensemble of different structures, then we can solve the problem completely. We started the calculation with the graphite-diamond transformation as a "seed", we know that this transformation is not observed in the experiment, but we were wondering what the calculation would do with this transformation. We waited a little (in fact, this calculation took half a year on a supercomputer) - and instead of a diamond, the calculation gave us M-carbon.

In general, I must say, I am an extremely lucky person, I had 1/40 chances of winning, because there were about 40 structures that had equal chances to win, but again I pulled out a lottery ticket. Our M-carbon won, we published our results in the prestigious new journal Scientific Reports, the new journal of the Nature group, and a month after we published our theoretical results, the results of a high-resolution experiment were published in the same journal, for the first time in 50 years. received. Yale University researchers did a high-resolution experiment and tested all these structures, and it turned out that only M-carbon satisfies all the experimental data. And now in the list of forms of carbon there is one more experimentally and theoretically established allotrope of carbon, M-carbon.

I will mention one more alchemical transformation. Under pressure, it is expected that all substances will turn into a metal, sooner or later any substance will become a metal. And what will happen to the substance, which was initially already a metal? For example, sodium. Sodium is not just a metal at all, but an amazing metal, described by the free electron model, that is, it is an extreme case of a good metal. What happens if you squeeze sodium? It turns out that sodium will no longer be a good metal - at first, sodium will turn into a one-dimensional metal, that is, electricity will only conduct in one direction. At higher pressures, we predicted that sodium would lose its metallicity altogether and turn into a reddish, transparent dielectric, and if the pressure was increased even further, it would become colorless like glass. So - you take a silvery metal, squeeze it - at first it turns into a bad metal, black as coal, squeeze further - it turns into a reddish transparent crystal that looks like a ruby, and then it becomes white like glass. We predicted this, and the journal Nature, where we sent it, refused to publish it. The editor returned the text within a few days and said: we do not believe it, it is too exotic. We found an experimenter, Mikhail Yeremets, who was ready to test this prediction, and here is the result. At 110 Gigapascals, that's 1.1 million atmospheres, it's still a silvery metal, at 1.5 million atmospheres, it's jet-black bad metal. At 2 million atmospheres, it is a transparent reddish non-metal. And already with this experiment, we published our results very easily. This, by the way, is a rather exotic state of matter, because the electrons are no longer spread out in space (as in metals) and are not localized on atoms or bonds (as in ionic and covalent substances) - valence electrons, which provided metallicity to sodium, are clamped in voids space, where there are no atoms, and they are very strongly localized. Such a substance can be called an electride, i.e. salt, where the role of negatively charged ions, anions, is played not by atoms (say, fluorine, chlorine, oxygen), but by bunches of electron density, and our form of sodium is the simplest and most striking example of an electride known.

Such calculations can also be used to understand the substance of the earth's and planetary interiors. We learn about the state of the earth's interior mainly from indirect data, from seismological data. We know that there is a metallic core of the Earth, mainly consisting of iron, and a non-metallic shell, consisting of magnesium silicates, called the mantle, and at the very surface there is a thin earth's crust on which we live, and which we know very well. Fine. And the interior of the Earth is almost completely unknown to us. By direct testing, we can only study the very, very surface of the Earth. The deepest well is the Kola Superdeep, its depth is 12.3 kilometers, drilled in the USSR, no one could drill further. The Americans tried to drill, went bankrupt on this project and stopped it. Huge sums were invested in the USSR, they drilled up to 12 kilometers, then perestroika happened, and the project was frozen. But the radius of the Earth is 500 times greater, and even the Kola super-deep well drilled only the very surface of the planet. But the substance of the Earth's depths determines the face of the Earth: earthquakes, volcanism, continental drift. The magnetic field is formed in the core of the Earth, which we will never reach. The convection of the molten outer core of the Earth is responsible for the formation of the Earth's magnetic field. By the way, the inner core of the Earth is solid, and the outer one is molten, it's like a chocolate candy with melted chocolate, and inside is a nut - this is how the core of the Earth can be imagined. The convection of the solid mantle of the Earth is very slow, its speed is about 1 centimeter per year; hotter flows go up, colder ones go down, and this is the convective movement of the Earth's mantle and is responsible for continental drift, volcanism, earthquakes.

An important question is what is the temperature at the center of the Earth? We know pressure from seismological models, but these models do not give temperature. The temperature is determined as follows: we know that the inner core is solid, the outer core is liquid, and that the core is made of iron. So if you know the melting point of iron at that depth, then you know the core temperature at that depth. Experiments were made, but they gave an uncertainty of 2 thousand degrees, and calculations were made, and the calculations put an end to this issue. The melting temperature of iron at the boundary of the inner and outer core was about 6.4 thousand degrees Kelvin. But when geophysicists learned about this result, it turned out that this temperature is too high to correctly reproduce the characteristics of the Earth's magnetic field - this temperature is too high. And then physicists remembered that, in fact, the core is not pure iron, but contains various impurities. What, we still do not know exactly, but among the candidates are oxygen, silicon, sulfur, carbon, hydrogen. By varying different impurities, comparing their effects, it was possible to understand that the melting point should be lowered by about 800 degrees. 5600 degrees Kelvin is such a temperature at the border of the inner and outer cores of the Earth, and this estimate is currently generally accepted. This effect of lowering the temperature by impurities, the eutectic lowering of the melting point, is well known, due to this effect, our shoes suffer in winter - roads are sprinkled with salt in order to lower the melting point of snow, and due to this, solid snow ice turns into a liquid state, and our shoes suffer from this salt water.

But perhaps the most powerful example of the same phenomenon is Wood's alloy - an alloy that consists of four metals, there are bismuth, lead, tin and cadmium, each of these metals has a relatively high melting point, but the effect of mutual lowering of the melting point works so hard that Wood's alloy melts in boiling water. Who wants to do this experience? By the way, I bought this sample of Wood's alloy in Yerevan on the black market, which, probably, will give this experience an additional flavor.

Pour boiling water, and I will hold the Wood's alloy, and you will see how the drops of Wood's alloy will fall into the glass.

Drops are falling - that's enough. It melts at the temperature of hot water.

And this effect occurs in the core of the Earth, due to this, the melting point of the ferrous alloy decreases. But now the next question is: what does the core consist of? We know that there is a lot of iron and some light elements-impurities, we have 5 candidates. We started with the least likely candidates, carbon and hydrogen. I must say that until recently, few people paid attention to these candidates, both were considered unlikely. We decided to check it out. Together with an employee of Moscow State University Zulfiya Bazhanova, we decided to take on this task, to predict the stable structures and stable compositions of iron carbides and hydrides under the conditions of the Earth's core. We also did this for silicon, where we did not find any special surprises - and for carbon, it turned out that those compounds that were considered stable for many decades, in fact, turn out to be unstable at the pressures of the Earth's core. And it turns out that carbon is a very good candidate, in fact, carbon alone can explain many properties of the Earth's inner core perfectly, contrary to previous work. Hydrogen, on the other hand, turned out to be a rather poor candidate; not a single property of the Earth's core can be explained by hydrogen alone. Hydrogen may be present in small amounts, but it cannot be the main impurity element in the Earth's core. For pressurized hydrogen hydrides, we found a surprise - it turned out that there is a stable compound with a formula that contradicts school chemistry. A normal chemist will write the formulas of hydrogen hydrides as FeH 2 and FeH 3 , generally speaking, FeH also appears under pressure, and they put up with it - but the fact that FeH 4 can form under pressure was a real surprise. If our kids at school write down the FeH 4 formula, I guarantee they will get an A in Chemistry, most likely even in a quarter. But it turns out that under pressure, the rules of chemistry are violated - and such exotic compounds appear. But, as I said, iron hydrides are unlikely to be important for the interior of the Earth, it is unlikely that hydrogen is present there in significant quantities, but carbon is most likely present.

And, finally, the last illustration, about the Earth's mantle, or rather, about the border between the core and the mantle, the so-called D layer, which has very strange properties. One of the properties was the anisotropy of the propagation of seismic waves, sound waves: in the vertical direction and in the horizontal direction, the velocities differ significantly. Why is it so? For a long time I couldn't understand. It turns out that a new structure of magnesium silicate is formed in the layer at the boundary of the Earth's core and mantle. We managed to understand this 8 years ago. At the same time, we and our Japanese colleagues published 2 papers in Science and Nature, which proved the existence of this new structure. It can be seen immediately that this structure looks completely different in different directions, and its properties must differ in different directions - including the elastic properties that are responsible for the propagation of sound waves. With the help of this structure, it was possible to explain all those physical anomalies that were discovered and caused trouble for many, many years. I even managed to make some predictions.

In particular, smaller planets such as Mercury and Mars will not have a layer like the D layer.” There is not enough pressure to stabilize this structure. It was also possible to make a prediction that as the Earth cools, this layer should grow, because the stability of post-perovskite increases with decreasing temperature. It is possible that when the Earth was formed, this layer did not exist at all, and it was born in the early phase of the development of our planet. And now all this can be understood thanks to the predictions of new structures of crystalline substances.

Reply from the audience: Thanks to the genetic algorithm.

Artem Oganov: Yes, although this last story about post-perovskite preceded the invention of this evolutionary method. By the way, she prompted me to invent this method.

Reply from the audience: So this genetic algorithm is 100 years old, they just didn’t do anything there.

Artem Oganov: This algorithm was created by me and my graduate student in 2006. By the way, calling it "genetic" is wrong, the more correct name is "evolutionary". Evolutionary algorithms appeared in the 70s, and they have found application in many areas of technology and science. For example, cars, ships and planes are optimized using evolutionary algorithms. But for each new task, the evolutionary algorithm is completely different. Evolutionary algorithms are not one method, but a huge group of methods, a whole huge area of ​​applied mathematics, and for each new type of problem, a new approach must be invented.

Reply from the audience: What math? It's genetics.

Artem Oganov: It's not genetics, it's mathematics. And for each new task, you need to invent your new algorithm from scratch. And people actually tried to invent evolutionary algorithms before us and adapt them to predict crystal structures. But they took algorithms from other areas too literally - and it didn't work, so we had to create a new method from scratch, and it turned out to be very powerful. Although the field of evolutionary algorithms has been around for about as long as I have, at least since 1975, crystal structure prediction has taken quite a bit of effort to create a working method.

All these examples that I gave you show how understanding the structure of matter and the ability to predict the structure of matter lead to the design of new materials that can have interesting optical properties, mechanical properties, electronic properties. Materials that make up the interior of the Earth and other planets. In this case, you can solve a whole range of interesting tasks on a computer using these methods. A huge contribution to the development of this method and its application was made by my employees and more than 1000 users of our method in different parts of the world. Let me sincerely thank all these people and the organizers of this lecture, and you - for your attention.

Lecture discussion

Boris Dolgin: Thanks a lot! Thank you very much, Artem, thank you very much to the organizers who gave us a platform for this version of public lectures, thank you very much to RVC, which supported us in this initiative, I am sure that Artyom’s research will continue, which means that we will have new material for his lecture, here , because it must be said that some of what was said today did not actually exist at the time of the previous lectures, so it makes sense.

Question from the floor: Tell me, please, how to ensure room temperature at such a high pressure? Any system of plastic deformation is accompanied by heat release. Unfortunately, you didn't say so.

Artem Oganov: The fact is that it all depends on how fast you compress. If compression is carried out very quickly, for example, in shock waves, then it is necessarily accompanied by heating, sharp compression necessarily leads to an increase in temperature. If you do the compression slowly, then the sample has enough time to exchange heat with its environment and come into thermal equilibrium with its environment.

Question from the floor: And your setup allows you to do this?

Artem Oganov: The experiment was not carried out by me, I did only calculations and theory. I do not allow myself to experiment due to internal censorship. And the experiment was carried out in chambers with diamond anvils, where a sample is squeezed between two small diamonds. In such experiments, the sample has so much time to reach thermal equilibrium that the question does not arise here.

The essence of the search for the most stable structure is reduced to the calculation of such a state of matter, which has the lowest energy. The energy in this case depends on the electromagnetic interaction of the nuclei and electrons of the atoms that make up the crystal under study. It can be estimated using quantum mechanical calculations based on a simplified Schrödinger equation. So the USPEX algorithm uses density functional theory which was developed in the second half of the last century. Its main purpose is to simplify calculations of the electronic structure of molecules and crystals. The theory makes it possible to replace the many-electron wave function by the electron density, while remaining formally exact (but in fact, approximations turn out to be inevitable). In practice, this leads to a decrease in the complexity of calculations and, as a result, the time that will be spent on them. Thus, quantum mechanical calculations are combined with the evolutionary algorithm in USPEX (Fig. 2). How does the evolutionary algorithm work?

You can look for structures with the lowest energy by enumeration: randomly arrange atoms relative to each other and analyze each such state. But since the number of options is huge (even if there are only 10 atoms, then there will be about 100 billion possibilities for their arrangement relative to each other), the calculation would take too long. Therefore, scientists managed to achieve success only after developing a more cunning method. The USPEX algorithm is based on an evolutionary approach (Fig. 2). First, a small number of structures are randomly generated and their energy calculated. Options with the highest energy, that is, the least stable, the system removes, and from the most stable generates similar ones and already calculates them. At the same time, the computer continues to randomly generate new structures to maintain the diversity of the population, which is an essential condition for successful evolution.

Thus, logic taken from biology helped to solve the problem of predicting crystal structures. It is difficult to say that there is a gene in this system, because new structures can differ from their predecessors in very different ways. The “individuals” most adapted to the selection conditions leave offspring, that is, the algorithm, learning from its mistakes, maximizes the chances of success in the next attempt. The system rather quickly finds the option with the lowest energy and effectively calculates the situation when a structural unit (cell) contains tens and even the first hundreds of atoms, while previous algorithms could not cope even with ten.

One of the new challenges facing USPEX at MIPT is the prediction of the tertiary structure of proteins from their amino acid sequence. This problem of modern molecular biology is one of the key ones. In general, the task before scientists is very difficult, also because it is difficult to calculate the energy for such a complex molecule as a protein. According to Artem Oganov, his algorithm is already able to predict the structure of peptides about 40 amino acids long.

Video 2. Polymers and biopolymers. What substances are polymers? What is the structure of a polymer? How widespread is the use of polymeric materials? Professor, PhD in Crystallography Artem Oganov talks about this.

USPEX Explanation

In one of his popular science articles, Artem Oganov (Fig. 3) describes USPEX as follows:

“Here is a figurative example to demonstrate the general idea. Imagine that you need to find the highest mountain on the surface of an unknown planet, where complete darkness reigns. In order to save resources, it is important to understand that we do not need a complete relief map, but only its highest point.

Figure 3. Artem Romaevich Oganov

You land a small force of biorobots on the planet, sending them one by one to random places. The instruction that each robot must follow is to walk along the surface against the forces of gravitational attraction and eventually reach the top of the nearest hill, the coordinates of which it must report to the orbital base. We have no funds for a large research contingent, and the likelihood that one of the robots will immediately climb the highest mountain is extremely small. This means that it is necessary to apply the well-known principle of Russian military science: “fight not by numbers, but by skill”, which is implemented here in the form of an evolutionary approach. Finding the nearest neighbor, the robots meet and reproduce their own kind, placing them along the line between "their" peaks. The offspring of biorobots start to follow the same instructions: they move in the direction of the elevation of the relief, exploring the area between the two peaks of their "parents". Those “individuals” that have come across peaks below the average level are recalled (this is how selection is carried out) and landed again randomly (this is how the maintenance of the “genetic diversity” of the population is modeled) ” .

How to estimate the error with which USPEX works? You can take a problem with the correct answer known in advance and solve it independently 100 times using an algorithm. If the correct answer is obtained in 99 cases, then the probability of a calculation error will be 1%. Usually correct predictions are obtained with a probability of 98–99% when the number of atoms in a unit cell is 40 pieces.

The USPEX evolutionary algorithm has led to many interesting discoveries and even to the development of a new dosage form of a medical product, which will be discussed below. I wonder what will happen when new generation supercomputers appear? Will the algorithm for predicting crystal structures change radically? For example, some scientists are engaged in the development of quantum computers. In the future, they will be much more efficient than the most advanced modern ones. According to Artem Oganov, evolutionary algorithms will retain their leading position, but will start to work faster.

Areas of work of the laboratory: from thermoelectrics to drugs

USPEX turned out to be an algorithm not only effective, but also multifunctional. At the moment, under the leadership of Artem Oganov, a lot of scientific work is being carried out in various areas. Some of the latest projects are attempts to model new thermoelectric materials and predict the structure of proteins.

“We have several projects, one of them is the study of low-dimensional materials such as nanoparticles, material surfaces, The other is the study of chemicals under high pressure. There is another interesting project related to the prediction of new thermoelectric materials. Now we already know that the adaptation of the crystal structure prediction method that we came up with to the problems of thermoelectrics works effectively. At the moment, we are already ready for a big breakthrough, the result of which should be the discovery of new thermoelectric materials. It is already clear that the method that we have created for thermoelectrics is very powerful, the tests carried out are successful. And we are fully prepared to look for actually new materials. We are also engaged in the prediction and study of new high-temperature superconductors. We ask ourselves the question of predicting the structure of proteins. This is a new challenge for us and a very interesting one.”

Interestingly, USPEX has already benefited even medicine: “Moreover, we are developing new medicines. In particular, we predicted, received and patented a new drug,- says A.R. Oganov. - It is 4-aminopyridine hydrate, a drug for multiple sclerosis".

We are talking about a drug recently patented by Valery Royzen (Fig. 4), Anastasia Naumova and Artem Oganov, a member of the Laboratory for Computer Design of Materials, which allows symptomatic treatment of multiple sclerosis. The patent is open, which will help reduce the price of the drug. Multiple sclerosis is a chronic autoimmune disease, that is, one of those pathologies when the host's own immune system harms the host. This damages the myelin sheath of nerve fibers, which normally performs an electrically insulating function. It is very important for the normal functioning of neurons: the current through the outgrowths of nerve cells covered with myelin is carried out 5–10 times faster than through uncovered ones. Because multiple sclerosis leads to disruption of the nervous system.

The underlying causes of multiple sclerosis remain unclear. Many laboratories around the world are trying to understand them. In Russia, this is done by the biocatalysis laboratory at the Institute of Bioorganic Chemistry.

Figure 4. Valery Roizen - one of the authors of a patent for a drug for multiple sclerosis, an employee of the Laboratory of Computer Design of Materials, who develops new dosage forms of medicines and is actively involved in the popularization of science.

Video 3. Popular science lecture by Valery Roizen "Delicious crystals". You will learn about the principles of how drugs work, the importance of the form of drug delivery to the human body, and the evil twin brother of aspirin.

Previously, 4-aminopyridine was already used in the clinic, but scientists managed to improve the absorption of this drug into the blood by changing the chemical composition. They obtained a crystalline 4-aminopyridine hydrate (Fig. 5) with a 1:5 stoichiometry. In this form, the drug itself and the method of obtaining it were patented. The substance improves the release of neurotransmitters in neuromuscular synapses, which makes it easier for patients with multiple sclerosis to feel better. It is worth noting that this mechanism involves the treatment of symptoms, but not the disease itself. In addition to bioavailability, the fundamental point in the new development is the following: since it was possible to “conclude” 4-aminopyridine in a crystal, it has become more convenient for use in medicine. Crystalline substances are relatively easy to obtain in a purified and homogeneous form, and the freedom of the drug from potentially harmful impurities is one of the key criteria for a good drug.

Discovery of new chemical structures

As mentioned above, USPEX allows you to find new chemical structures. It turns out that even “usual” carbon has its own mysteries. Carbon is a very interesting chemical element because it forms a wide range of structures ranging from superhard dielectrics to soft semiconductors and even superconductors. The former include diamond and lonsdaleite, the latter - graphite, and the third - some fullerenes at low temperatures. Despite the wide variety of known forms of carbon, scientists led by Artem Oganov managed to discover a fundamentally new structure: it was not previously known that carbon can form guest-host complexes (Fig. 6). The work was also attended by employees of the laboratory of computer-aided design of materials (Fig. 7).

Figure 7. Oleg Feya, MIPT PhD student, employee of the Laboratory of Computer Design of Materials and one of the authors of the discovery of a new carbon structure. In his free time, Oleg is engaged in the popularization of science: his articles can be read in the publications Schrödinger's Cat, For Science, STRF.ru, Rosatom Country. In addition, Oleg is the winner of the Moscow science slam and a participant in the TV show "The Smartest".

The "guest-host" interaction manifests itself, for example, in complexes consisting of molecules that are connected to each other by non-covalent bonds. That is, a certain atom / molecule occupies a certain place in the crystal lattice, but does not form a covalent bond with the surrounding compounds. This behavior is widespread among biological molecules that bind to each other to form strong and large complexes that perform various functions in our body. In general, we mean compounds consisting of two types of structural elements. For substances formed only by carbon, such forms were not known. Scientists published their discovery in 2014, expanding our knowledge about the properties and behavior of the 14th group of chemical elements in general (Fig. 8). It is worth noting that in the open form of carbon, covalent bonds between atoms are formed. We are talking about the guest-host type because of the presence of clearly defined two types of carbon atoms, which have completely different structural environments.

New high pressure chemistry

In the laboratory of computer-aided materials design, they study which substances will be stable at high pressures. Here is how the head of the laboratory argues for interest in such research: “We are studying materials under high pressure, in particular the new chemistry that appears under such conditions. This is a very unusual chemistry that does not fit into the rules of the traditional. The knowledge gained about new compounds will lead to an understanding of what is happening inside the planets. Because these unusual chemicals can prove to be very important materials in the interior of the planet.” It is difficult to predict how substances behave under high pressure: most of the chemical rules stop working, because these conditions are very different from what we are used to. Nevertheless, this must be understood if we want to know how the Universe works. The lion's share of the baryonic matter of the Universe is under high pressure inside the planets, stars, satellites. Surprisingly, very little is known about its chemistry.

The new chemistry, which is implemented at high pressure in the laboratory of computer-aided design of materials at MIPT, is being studied by Gabriele Saleh, a PhD (degree similar to a Ph.D.):

“I am a chemist and I am interested in chemistry at high pressures. Why? Because we have rules of chemistry that were formulated 100 years ago, but recently it turned out that they stop working at high pressures. And it's very interesting! It's like an amusement park: there is a phenomenon that no one can explain; exploring a new phenomenon and trying to understand why it happens is very interesting. We started the conversation with fundamental things. But high pressures exist in the real world as well. Of course, not in this room, but inside the Earth and on other planets. .

Since I'm a chemist I'm interested in high-pressure chemistry. Why? Because we have chemical rules which were established one hundred years ago but recently it was discovered that these rules get broken at high pressure. And it is very interesting! This is like a loonopark because you have a phenomenon, which nobody can rationalize. It's interesting to study new phenomenon and to try to understand why does it happen. We started from the fundamental point of view. But these high pressures exist. Not in this room of course but in the inside of the Earth and in other planets.

Figure 9. Carbonic acid (H 2 CO 3) is a pressure stable structure. Inserted on top shown that along C axis polymer structures are formed. The study of the carbon-oxygen-hydrogen system under high pressures is very important for understanding how the planets are arranged. H 2 O (water) and CH 4 (methane) are the main constituents of some giant planets - for example Neptune and Uranus, where the pressure can reach hundreds of GPa. Large icy satellites (Ganymede, Callisto, Titan) and comets also contain water, methane and carbon dioxide, which are subjected to pressure up to several GPa.

Gabriele told us about his new work, which was recently accepted for publication:

“Sometimes you do basic science, but then you find a direct application of the knowledge gained. For example, we recently submitted an article for publication describing the results of a search for all stable compounds produced from carbon, hydrogen, and oxygen at high pressure. We have found one that is stable at very low pressures such as 1 GPa. , and it turned out to be carbonic acid H 2 CO 3(Fig. 9). I studied the literature on astrophysics and found that the moons of Ganymede and Callisto [moons of Jupiter] are composed of water and carbon dioxide: molecules that form carbonic acid. Thus we realized that our discovery suggests the formation of carbonic acid there. This is what I was talking about: it all started with basic science and ended up with something important for the study of satellites and planets. ” .

Note that such pressures turn out to be low relative to those that can in principle be found in the Universe, but high compared to those that act on us near the surface of the Earth.

So sometimes you study something for fundamental science but then you discover it has a right application. For example, we have just submitted a paper in which we took carbon, hydrogen, oxygen at high pressure and we tried to look for the all stable compounds. We found one which was carbonic acid and it was stable in a very low pressure like one gigapascal. I investigate the astrophysics literature and discovered: there are satellites such as Ganymede or Calisto. On them there is carbon dioxide and water. The molecules which form this carbonic acid. So we realized that this discovery means that probably there would be carbonic acid. This is what I mean by started for fundamental and discovering something which is applicable to planetary science.

Another example of unusual chemistry that can be given concerns the well-known table salt, NaCl. It turns out that if you can pressurize your salt shaker to 350 GPa, you'll get new compounds. In 2013, under the leadership of A.R. Oganov, it was shown that if high pressure is applied to NaCl, then unusual compounds become stable - for example, NaCl 7 (Fig. 10) and Na 3 Cl. Interestingly, many of the discovered substances are metals. Gabriele Saleh and Artem Oganov continued pioneering work in which they showed the exotic behavior of sodium chlorides under high pressure and developed a theoretical model that can be used to predict the properties of alkali metal compounds with halogens.

They described the rules that these substances obey under such unusual conditions. Using the USPEX algorithm, several compounds with the formula A 3 Y (A = Li, Na, K; Y = F, Cl, Br) were theoretically subjected to pressures up to 350 GPa. This led to the discovery of chloride ions in the oxidized state −2. "Standard" chemistry forbids this. Under such conditions, new substances can be formed, for example, with the chemical formula Na 4 Cl 3.

Figure 10. Crystal structure of common NaCl salt ( left) and the unusual compound NaCl 7 ( on right), stable under pressure.

Chemistry needs new rules

Gabriele Saleh (Fig. 11) spoke about his research aimed at describing new rules of chemistry that would have predictive power not only under standard conditions, but would describe the behavior and properties of substances under high pressure (Fig. 12).

Figure 11. Gabriele Saleh

“Two or three years ago, Professor Oganov discovered that such a simple salt as NaCl is not so simple under high pressure: sodium and chlorine can also form other compounds. But no one knew why. Scientists performed calculations, received results, but it remained unknown why everything happens this way and not otherwise. I have been studying chemical bonding since graduate school, and in the course of my research, I was able to formulate some rules that logically explain what is happening. I studied how electrons behave in these compounds and came up with general patterns that are characteristic of them under high pressure. In order to test whether these rules are a figment of my imagination or are still objectively true, I predicted the structures of similar compounds - LiBr or NaBr, and a few more similar ones. Indeed, the general rules apply. In short, I have seen that there is a tendency that when you apply pressure to such joints, they form a two-dimensional metal structure, and then one-dimensional. Then, under very high pressure, wilder things start to happen because chlorine would then have an oxidation state of -2. All chemists know that chlorine has an oxidation state of -1, this is a typical textbook example: sodium loses an electron, and chlorine takes it. Therefore, the oxidation numbers are +1 and −1, respectively. But under high pressure, things don't work that way. We have shown this with the help of some approaches for the analysis of chemical bonds. Also in the course of work, I searched for special literature to understand if anyone had already observed such patterns. And it turned out that yes, they did. If I am not mistaken, sodium bismuthate and some other compounds obey the rules described. Of course, this is just the beginning. When the next papers on the topic are published, we will find out if our model has real predictive power. Because that's exactly what we're looking for. We want to describe chemical laws that would hold even at high pressures.” .

Two or three years ago professor Oganov discovered that the simple salt NaCl at high pressure is not very simple and other compounds will form. But no one knows why. They made a calculation they got the results but you cannot say why this is happening. So since during my PhD I specializing in the study of chemical bonding, I investigate this compounds and I find some rule to rationalize what is going on. I how electrons investigate behave in this compounds and I came up with some rules which these kinds of compounds will follow at high pressure. To check whether my rules were just my imagination or they were true I predicted new structures of similar compounds. For example LiBr or NaBr and some combinations like this. And yes, these rules turn out to be followed. In short, just not to be very specialistic, I’ve seen that there is a tendency: when you compress them they would form two-dimensional metals, then one-dimensional structure of metal. And then at very high pressure some more wild would happen because the Cl in this case will have the oxidation number of −2. All the chemist know that the lowest oxidation number of Cl is −1, which is a typical textbook example: sodium loses electron and chlorine gets it. So we have +1 and −1 oxidation numbers. But at a very high pressure it is not true anymore. We demonstrated this with some approaches for chemical bonding analysis. In that work also I tried to look at the literature to if somebody have seen this kind of rules before. And yes, it turned out that there were some. If I'm not mistaken, Na-Bi and other compounds turned out to follow these rules. It is just a starting point, of course. The other papers will come up and we will see whether this model has a real predictive power. Because this is what we are looking for. We want to sketch the chemistry which will work also for high pressure.

Figure 12. The structure of a substance with the chemical formula Na 4 Cl 3 , which is formed at a pressure of 125-170 GPa, which clearly demonstrates the appearance of "strange" chemistry under pressure.

If you experiment, then selectively

Despite the fact that the USPEX algorithm has great predictive power within its tasks, the theory always requires experimental verification. The Computer Materials Design Lab is theoretical, as even its name implies. Therefore, experiments are carried out in cooperation with other scientific teams. Gabriele Saleh comments on the research strategy adopted in the laboratory as follows:

“We do not conduct experiments - we are theorists. But often we cooperate with people who do it. In fact, I think it's generally difficult. Today, science is highly specialized, so it’s not easy to find someone who does both.” .

We don't do experiments, but often we collaborate with some people who do experiments. Actually I think in fact it's hard. Nowadays the science is very specialized so it's hard to find somebody who does both.

One of the clearest examples is the prediction of transparent sodium. In 2009 in the magazine Nature the results of the work carried out under the direction of Artem Oganov were published. In the article, the scientists described a new form of Na, in which it is a transparent non-metal, becoming a dielectric under pressure. Why is this happening? This is due to the behavior of valence electrons: under pressure, they are forced out into the voids of the crystal lattice formed by sodium atoms (Fig. 13). In this case, the metallic properties of the substance disappear and the qualities of the dielectric appear. A pressure of 2 million atmospheres makes sodium red, and 3 million atmospheres makes it colorless.

Figure 13. Sodium under pressure over 3 million atmospheres. in blue shows the crystal structure of sodium atoms, orange- bunches of valence electrons in voids of the structure.

Few believed that classical metal could exhibit such behavior. However, in collaboration with the physicist Mikhail Yeremets, experimental data were obtained that completely confirmed the prediction (Fig. 14).

Figure 14. Photographs of a Na sample taken with a combination of transmitted and reflected illumination. Different pressures were applied to the sample: 199 GPa (transparent phase), 156 GPa, 124 GPa, and 120 GPa.

You have to work with fire!

Artem Oganov told us what requirements he places on his employees:

“First, they must have a good education. Second, be hardworking. If a person is lazy, then I won’t hire him, and if I suddenly hire him by mistake, he will be kicked out. I simply fired several employees who turned out to be lazy, inert, amorphous. And I think that this is absolutely right and good even for the person himself. Because if a person is not in his place, he will not be happy. He needs to go where he will work with a twinkle, with enthusiasm, with pleasure. And this is good for the laboratory, and good for the person. And those guys who really work beautifully, with a twinkle, we pay good salaries, they go to conferences, they write articles that are then published in the best world magazines, everything will be fine with them. Because they are in the right place and because the laboratory has good resources to support them. That is, the guys do not need to think about earning money in order to survive. They can concentrate on science, on their favorite business, and successfully do it. We now have some new grants, and this opens up the possibility for us to hire a few more people. There is competition all the time. People apply all year round, but of course, I don’t accept all of them.”. (2016). 4-Aminopyridine crystalline hydrate, method for its preparation, pharmaceutical composition and method for treatment and/or prevention based on it. Phys. Chem. Chem. Phys. 18 , 2840–2849;

- Let's deal with the computer design of new materials. First, what is it? Area of ​​knowledge? When does the idea and this approach appear?

— The region is quite new, it is only a few years old. In itself, the computer-aided design of new materials has been the dream of researchers, technologists, and fundamental scientists for many decades. Because the process of discovering a new material with the properties you need usually takes many years or even decades of work of entire institutes and laboratories. This is a very costly process, at the end of which you may be disappointed. That is, you are not always able to invent such material. But even when you achieve success, success can take many years of work. This does not suit us at all now, we want to invent new materials, new technologies as quickly as possible.

- Can you give an example of such a material that cannot be or could not be invented?

- Yes, sure. For example, for many decades people have been trying to come up with a material harder than diamond. There have been hundreds of publications on this subject. In some of them, people claimed that they found a material harder than diamond, but then inevitably, after some time (usually not very long), these claims were refuted, and it turned out that this was an illusion. Until now, no such material has been found, and it is quite clear why. With the help of our methods, we were able to show that this is fundamentally impossible, so there is no time to waste.

- And if you try to just explain why not?

- A property such as hardness has a finite limit for each given material. If we take all the materials that are possible to take, then it turns out that there is a certain global upper limit. It just so happens that this upper limit corresponds to a diamond. Why a diamond? Because several conditions are simultaneously fulfilled in this structure: very strong chemical bonds, a very high density of these chemical bonds, and they are evenly distributed in space. There is no one direction that is much harder than the other, it is a very hard substance in all directions. The same graphite, for example, has stronger bonds than diamond, but all these bonds are located in the same plane, and very weak bonds interact between the planes, and this weak direction makes the whole crystal soft.

- How did the method develop and how did scientists try to improve it?

- The great Edison said, in my opinion, in connection with his invention of the incandescent light bulb: "I did not fail ten thousand times, but only found ten thousand ways that do not work." This is the traditional style of searching for new materials, which is called Edisonian in the scientific literature. And, of course, people have always wanted to move away from this method, because it requires a rare Edisonian luck and Edisonian patience. And a lot of time as well as money. This method is not very scientific, it is rather a scientific "poke". And people have always wanted to get away from it. When computers appeared and they began to solve more or less complex problems, the question immediately arose: “Can all these combinations of different conditions, temperatures, pressures, chemical potentials, chemical composition be sorted out on a computer instead of doing it in a laboratory?” Expectations were very high at first. People looked at it a little optimistic and euphoric, but soon all these dreams were shattered into everyday life. By the methods by which people tried to solve the problem, nothing can be achieved in principle.

- Why?

“Because there are infinitely many options for different arrangements of atoms in the structure of a crystal, and each of them will have completely different properties. For example, diamond and graphite are the same substance, and due to the fact that the structure is different, their properties are radically different. So there can be an infinite number of different options that differ from both diamond and graphite. What will you start with? Where will you stop? How long will it last? And if you also introduce a variable of chemical composition, then you can also come up with an infinite number of different chemical compositions, and the task becomes unbearably difficult. Very quickly, people realized that traditional, standard methods for solving this problem lead to absolutely nothing. This pessimism completely buried the first hopes that people had cherished since the 60s.

— Computer design is still conceived or at least felt as a visual thing. As I understand it, in the 60s, 70s or 80s, this is still not a visual solution, but a mathematical one, that is, it is a faster calculation, calculation.

- As you understand, when you get numbers on a computer, you can always visualize them, but this is not the only thing.

- In general, it is only a question of the readiness of technology to do this.

- Yes. Numerical counting is primary, because you can always make a picture out of numbers, and you can probably make numbers out of a picture, too, although not very accurate. There were a number of famous publications from the mid-80s to the mid-90s, which finally instilled pessimism in our field. For example, there was a wonderful publication that said that even such simple substances as graphite or ice are absolutely impossible to predict. Or there was an article called "Are Crystal Structures Predictable" and the first word of that article was "no".

What does "predictable" mean?

— The task of predicting the crystal structure is the core of the entire field of design of new materials. Since structure determines the properties of a substance, in order to predict a substance with the desired properties, one must predict the composition and structure. The problem of predicting the crystal structure can be formulated as follows: suppose that we have given the chemical composition, suppose it is fixed, for example, carbon. What will be the most stable form of carbon under given conditions? Under normal conditions, we know the answer - it will be graphite; at high pressures, we also know the answer - it's a diamond. But creating an algorithm that could give you that is proving to be a very difficult task. Or you can formulate the problem in a different way. For example, for the same carbon: what would be the hardest structure corresponding to this chemical composition? It turns out a diamond. Now let's ask another question: what will be the densest? It seems that it is also a diamond, but not. It turns out that a form of carbon denser than diamond can be invented, at least on a computer, and in principle it can be synthesized. Moreover, there are many such hypothetical forms.

- Even so?

- Even so. But nothing is harder than a diamond. People have learned to get answers to such questions quite recently. More recently, algorithms have appeared, programs have appeared that can do this. In this case, in fact, this entire area of ​​research turned out to be connected with our work in 2006. After that, many other researchers also began to deal with this problem. In general, we still do not lose the palm and come up with more and more methods, new and new materials.

- "Who are "we?

— This is me and my students, graduate students and researchers.

— To make it clear, because “we” is so polysemantic, in this case polysemantic, it can be perceived in different ways. What is so revolutionary?

— The fact is that people have realized that this task is associated with an infinitely complex combinatorial problem, that is, the number of options among which you need to choose the best is infinite. How can this problem be solved? No way. You can simply not approach her and feel comfortable. But we have found a way that this problem can be solved quite effectively - a way based on evolution. This, one might say, is a method of successive approximations, when from initially weak solutions by the method of successive improvement we come to more and more perfect solutions. We can say that this is an artificial intelligence method. Artificial intelligence, which makes a number of assumptions, rejects some of them, and constructs even more interesting ones from the most plausible, most interesting structures and compositions. That is, he learns from his own history, which is why it can be called artificial intelligence.

- I would like to understand how you invent, invent new materials on a specific example.

— Let's try to describe it on the example of the same carbon. You want to predict which form of carbon is the hardest. A small number of random carbon structures are specified. Some structures will consist of discrete molecules, like fullerenes; some structures will consist of layers, like graphite; some will consist of carbon chains, the so-called carbines; some will be three-dimensionally connected, like a diamond (but not only a diamond, there are an infinite number of such structures). You randomly generate these kinds of structures first, then you do local optimization, or what we call "relaxation". That is, you move the atoms until the resulting force on the atom is zero, until all stresses in the structure disappear, until it enters its ideal form or picks up its best local shape. And for this structure, you calculate properties, such as hardness. Let's look at the hardness of fullerenes. There are strong bonds, but only within the molecule. The molecules themselves are interconnected very weakly, due to this, the hardness is almost zero. Look at graphite - the same story: strong bonds within the layer, weak between the layers, and as a result, the substance disintegrates very easily, its hardness will be very small. Substances such as fullerenes or carbines or graphite will be very soft, and we immediately reject them. The remaining structures of carbon are three-dimensionally connected, they have strong bonds in all three dimensions, from these structures we choose the most solid ones and give them the opportunity to produce daughter structures. What does it look like? We take one structure, take another structure, cut out their pieces, assemble them together, as in a constructor, and again relax, that is, we give the opportunity for all stresses to go away. There are mutations - this is another way to produce offspring from parents. We take one of the most solid structures and mutate it, for example, we apply a huge shear stress so that some bonds there simply burst, while others, new ones, are formed. Or we shift the atoms in the weakest directions of the structure in order to remove this weakness from the system. We relax all structures produced in this way, that is, we remove internal stresses, and after that we again evaluate the properties. It happens that we took a solid structure, mutated it, and it became soft, turned into, say, graphite. We remove this structure immediately. And from those that are solid, we again produce “children”. And so we repeat step by step, generation after generation. And fast enough we come to the diamond.

- At the same time, the moments when we reject, compare, connect and change the structure, do artificial intelligence, do the program? Not a human?

- The program does it. If we did this, we would end up in Kashchenko, because this is a huge number of operations that a person does not need to do and for completely scientific reasons. You understand, a person is born, absorbs experience from the surrounding world, and with this experience comes a kind of prejudice. We see a symmetrical structure - we say: "This is good"; we see asymmetric - we say: "This is bad." But for nature, sometimes the opposite is true. Our method must be free from human subjectivity and prejudice.

- Do I understand correctly from what you described that, in principle, this task is formulated not so much by fundamental science as by the solution of quite specific tasks set by some regular transnational company? Here we need new cement to be more viscous, denser or, conversely, more liquid, and so on.

- Not at all. In fact, I came from fundamental science in my education, I studied fundamental science, not applied science. I am now interested in solving applied problems, especially since the methodology that I invented is applicable to the most important applied problems of a very wide range. But initially this method was invented to solve fundamental problems.

- What kind of?

— I have been studying high-pressure physics and chemistry for a long time. This is an area in which many interesting discoveries have been made experimentally. But experiments are complex, and very often experimental results turn out to be wrong over time. Experiments are expensive and time-consuming.

- Give an example.

- For example, for a long time there was a race between Soviet and American scientists: who will get the first metallic hydrogen under pressure. Then it turned out, for example, that many simple elements under pressure become (this is such an alchemical transformation) a transition metal. For example, you take potassium: potassium has only one s-electron on the valence shell, and so under pressure it becomes a d-element; The s-orbital is emptied, and the unoccupied d-orbital is populated by this single electron. And this is very important, because potassium, becoming a transition metal, then gets the opportunity to enter, for example, into liquid iron. Why is it important? Because now we believe that potassium in small quantities is part of the Earth's core and is a source of heat there. The fact is that one of the isotopes of potassium (radioactive potassium-40) is one of the main producers of heat on Earth today. If potassium is not included in the Earth's core, then we must completely change our understanding of the age of life on Earth, the age of the magnetic field, the history of the Earth's core, and many other interesting things. Here is an alchemical transformation - s-elements become d-elements. At high pressures, when you compress matter, the energy that you spend on compression will sooner or later exceed the energy of chemical bonds and the energy of interorbital transitions in atoms. And thanks to this, you can radically change the electronic structure of the atom and the type of chemical bond in your substance. Completely new types of substances can arise. And the standard chemical intuition does not work in such cases, that is, the rules that we learn from the school bench in chemistry lessons, they fly into hell when the pressure reaches sufficiently large values. I can tell you what kind of things have been predicted by our method and then experimentally proven. When this method appeared, it became a shock for everyone. One of the most interesting works was related to the element sodium. We predicted that if we compress sodium to a pressure of about 2 million atmospheres (by the way, the pressure in the center of the Earth is almost 4 million atmospheres, and such pressures can be obtained experimentally), it will no longer be a metal, but a dielectric, moreover, transparent and red colors. When we made this prediction, no one believed us. The journal Nature, to which we sent these results, even refused to consider this article, they said that it was impossible to believe in it. I contacted the experimenters from the group of Mikhail Yeremets, who also told me that it was impossible to believe in this, but out of respect they would still try to conduct such an experiment. And this experiment fully confirmed our predictions. The structure of the new phase of the element boron was predicted - the hardest structure for this element, one of the hardest substances known to mankind. And there it turned out that different boron atoms have a different electric charge, that is, they suddenly become different: some are positively charged, some are negatively charged. This article has been cited almost 200 times in just three years.

You said that this is a fundamental task. Or do you primarily solve fundamental problems and only recently some practical issues? History of sodium. For what? That is, you sat and sat and thought what to take - I will take sodium, perhaps, and compress it into 2 million atmospheres?

- Not certainly in that way. I received a grant to study the behavior of the elements under high pressure in order to better understand the chemistry of the elements. Experimental data under high pressure is still very fragmentary, and we decided to go through more or less the entire Periodic Table to understand how the elements and their chemistry change under pressure. We have published a number of papers, in particular, on the nature of superconductivity in oxygen under pressure, since oxygen under pressure becomes a superconductor. For a number of other elements: alkaline elements or alkaline earth elements and so on. But the most interesting, probably, was the discovery of new phenomena in sodium and boron. These were perhaps the two elements that surprised us the most. That's how we started. And now we have moved on to solving practical problems, we are cooperating with companies such as Intel, Samsung, Fujitsu, Toyota, Sony. Toyota, as far as I know, has recently invented a new material for lithium batteries using our method and is going to put this material on the market.

- They took your method, they took the technology of searching for materials, but not you?

- Yes, sure. We do not impose ourselves in the load, but we try to help all researchers. Our program is available to anyone who wants to use it. Companies need to pay something for the right to use the program. And scientists working in academia get it for free by simply downloading it from our website. Our program already has almost 2 thousand users around the world. And I am very happy when I see that our users achieve something good. I, my group, have more than enough of my own discoveries, my own works, my own insights. When we see the same thing in other groups, it only pleases.

The material was prepared on the basis of the radio program "PostNauka" on the radio Russian News Service.