home Chimneys Computer synthesis of materials and gans. Laboratory of computer-aided design of materials: what can USPEX give? Areas of work of the laboratory: from thermoelectrics to drugs

Computer synthesis of materials and gans. Laboratory of computer-aided design of materials: what can USPEX give? Areas of work of the laboratory: from thermoelectrics to drugs

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. The structure of matter: atoms, molecules The ancients guessed that matter consists of particles: “when He (God) had not yet created the earth, nor the fields, nor the initial grains of dust of the universe” (Proverbs, 8:26) (also - Epicurus, Lucretius Carus , ancient Hindus,...) In 1611, J. Kepler suggested that the structure of ice, the shape of snowflakes, is determined by their atomic structure
3. The structure of matter: atoms, molecules, crystals 1669 - the birth of crystallography: Nicholas Stenon formulates the first quantitative law of crystallography “Crystallography... is unproductive, exists only for itself, has no consequences... not being truly needed anywhere, it developed 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 so long.” (I.V. Goethe, amateur crystallographer, 1749-1832) Ludwig Boltzmann (1844-1906) is a great Austrian physicist who based all his theories on ideas about atoms. Criticism of atomism led him to suicide in 1906. In 1912, the hypothesis about the atomic structure of matter was proven by the experiments of Max von Laue.
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. X-ray diffraction is the main method for experimental determination of crystal structure Structure Diffraction pattern
6. Relationship between structure and diffraction pattern What will the diffraction patterns of these “structures” be?
7. Triumphs of experiment - determination of incredibly complex crystal 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. States of matter Crystalline Quasicrystalline Amorphous Liquid Gaseous (“Soft matter” – polymers, liquid crystals)
9. Atomic structure is the most important characteristic of a substance. 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. Several stories 4. Materials of the earth's interior 3. Materials from a computer 2. Is it possible to predict crystalline ones? On the connection between structure, structure and properties
11. Why is ice lighter than water? The structure of ice contains large empty channels that are not present in liquid water. The presence of these empty channels makes the ice lighter than ice.
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 for the energy sector? 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. CO2 hydrate - a form of carbon dioxide burial? The mechanism of xenon anesthesia is the formation of Xe-hydrate, which blocks the transmission of neuronal signals to the brain (Pauling, 1951)
13. Microporous materials for the chemical industry and environmental cleanup Zeolites are microporous aluminosilicates. Separation of octane and iso-octane by zeolite is used in chemical applications. industry Historical examples of heavy metal poisoning: Qin Shi Huangdi Ivan IV the Terrible “Disease of Nero (37-68) Lead (259 – 210 BC) (1530-1584) insane poisoning: hatter” aggression, dementia
14. New and old superconductors The phenomenon was discovered in 1911 by Kamerlingh 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. 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 fullerene crystals C60 fullerite Superconductivity in organic crystals has been known since 1979 (Bechgaard, 1979).
16. How materials can save or destroy At low temperatures, tin undergoes a phase transition - the “tin plague”. 1812 - according to legend, Napoleon's expedition to Russia died because of tin buttons on their uniforms! 1912 – 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. 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, oil pipeline components and aircraft engines
18. Miracles of optical properties Pleochroism (cordierite) - discovery of America and navigation of the US Air Force Birefringence of light (calcite) Alexandrite effect (chrysoberyl) Chalice of Lycurgus (glass with nanoparticles)
19. About the nature of colorWavelength, Å Color Complementary color4100 Violet Lemon yellow4300 Indigo Yellow4800 Blue Orange5000 Blue-green Red5300 Green Purple5600 Lemon yellow Violet5800 Indigo Yellow6100 Orange Blue6800 Red Blue-green
20. Color depends on direction (pleochroism). Example: cordierite (Mg,Fe)2Al4Si5O18.
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. J. Maddox (Nature, 1988) The task is to find the GLOBAL minimum of Natom Variants Time energy. 1 1 1 sec. Enumeration of all structures is impossible: 10 1011 103 yrs. 20 1025 1017 yrs. 30 1039 1031 yrs. USPEX Method Overview (ARO & Glass, J.Chem.Phys. 2006)
23. How to find Mount Everest using kangaroo evolution? (picture from R. Clegg) We land kangaroos and allow them to breed (not shown for censorship reasons).....
24. How to find Mount Everest using kangaroo evolution? (picture from R.Clegg) Aaaargh! Ouch....and from time to time hunters come and remove kangaroos at lower altitudes
25.
26. Evolutionary calculations “self-learn” and focus the search on the most interesting areas of space
27. Evolutionary calculations “self-learn” and focus the search on the most interesting areas of space
28. Evolutionary calculations “self-learn” and focus the search on the most interesting areas of space
29. Evolutionary calculations “self-learn” and focus the search on the most interesting areas of space
30. Alternative methods: Random search (Freeman & Catlow, 1992; van Eijck & Kroon, 2000; Pickard & Needs, 2006) No “learning”, 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-dimensional space Minima hopping (Gödecker 2004) Uses calculation history and “self-learning”. Genetic and evolutionary algorithms Bush (1995), Woodley (1999) are an ineffective method for crystals. Deaven & Ho (1995) is an effective method for nanoparticles.
31. USPEX(Universal Structure Predictor: Evolutionary Xtallography) (Random) initial population A new generation of structures is produced only from the best current structures (1) Heredity (3) Coordinate (2) Lattice mutation mutation (4) Permutation
32. Additional techniques - order parameter “Fingerprint” of the structure The birth of order from chaos in the evolutionary process [“GOD = Generator Of Diversity” © S. Avetisyan] Local order – indicates defective areas
33. Test: “Who would guess that graphite is the stable allotrope of carbon at ordinary pressure?” (Maddox, 1988) Three-dimensional sp2 structure proposed Graphite was correctly predicted by R. Hoffmann (1983) as a stable phase at 1 atm Structures with low sp3- energy hybridization illustrate sp2 hybridization carbon chemistry sp hybridization (carbyne)
Test: High pressure phases are also reproduced correctly100 GPa: diamond is stable 2000 GPa: bc8 phase is stable + metastable phase found, explaining Metastable bc8 phase of silicon “superhard graphite” is known (Kasper, 1964) (Li, ARO, Ma, et al., PRL 2009)
35. Discoveries made with USPEX:
36. 3. Materials from the computer
37. Discovery of new materials: still an experimental method of trial and error “I have not suffered (ten thousand) failures, but only discovered 10,000 methods that did not work” (T. A. Edison)
38. Search for the densest substance: are modifications of carbon denser than diamond possible? Yes Structure of Diamond Diamond has the smallest atomic volume and the greatest incompressibility of all New structure, elements (and compounds). denser than diamond! (Zhu, ARO, et al., 2011)
39. The analogy of the forms of carbon and silica (SiO2) allows us 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 structureSiO2 cristobalite SiO2 quartz SiO2 kitite high pressure SiS2 phase
40.
41. The hardest oxide is TiO2? (Dubrovinsky et al., Nature 410, 653-654 (2001)) Nishio-Hamane (2010) and Al-Khatatbeh (2009): compressive modulus ~300 GPa, not 431 GPa. Lyakhov & ARO (2011): Experiments under pressure are very difficult! Hardness not higher than 16 GPa! TiO2 is softer than SiO2 stishovite (33 GPa), B6O (45 GPa), Al2O3 corundum (21 GPa).
42. Are there possible forms of carbon harder than diamond? 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 hybrid ization Evolutionary calculation
43. Cold compression of graphite produces 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 has been confirmed by the latest experiments M-carbon is most easily formed from graphite graphite bct4-carbon graphite M -carbon graphite diamond
44. M-carbon - a new form of carbon diamondgraphite lonsdaleite Theoretical phase diagram of carbon M-carbonfullerenes carbines
45. Substance under pressure in nature P.W. Bridgman 1946 Nobel Laureate (Physics) 200xScale: 100 GPa = 1 Mbar =
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 source of energy (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. Boron is between metals and non-metals and its unique structures are sensitive to B impurities, temperature and pressure alpha-B beta B T-192
48. The history of the discovery and research of boron is full of contradictions and detective twists 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 were published (most are compounds?). It is not known which form is the most stable. F. Wöhler
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: defined 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. The first phase diagram of boron - after 200 years of research! BBoron phase diagram (ARO et al., Nature 2009)
51. Sodium is a metal perfectly described by the free electron model
52. Under pressure, sodium changes its essence - “alchemical transformation” Na 1807: Sodium discovered by Humphry Davy. 2002: Hanfland, Syassen, et al. – the first indication of extremely complex chemistryH. Davy sodium under pressure over 1 Mbar. Gregoryants (2008) – more detailed data. Under pressure, sodium becomes partly a d-metal!
53. We predicted a new structure that 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, this makes compressed sodium a non-metal
The study of minerals is not only an aesthetic pleasure, but also a practically and fundamentally important scientific direction. The 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!
64. What is the composition of the Earth's inner core? The core is somewhat less dense than pure iron. In the core, Fe is alloyed 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 core in large quantities [Bazhanova, Oganov, Dzhanola, UFN 2012]. The percentage of carbon in the inner core needed to explain its density
65. The nature of layer D” (2700-2890 km) remained a mystery for a long time D” – the root of hot mantle flows It is expected that MgSiO3 makes up ~75 vol.% Oddities of layer D”: seismic rupture, anisotropy Let us remember the anisotropy of the color of cordierite!
66. The solution is the existence of a new mineral, MgSiO3 post-perovskite in layer D" (2700-2890 km) Phase diagram D" discontinuity MgSiO3 Explains the existence of layer D, allows you to calculate its temperature Explains variations in day length MgSiO3 Layer D" grows post- perovskite as Earth cools D“ absent from Mercury and Mars New family of minerals predicted Confirmation – Tschauner (2008)
67. The structure of matter is the key to understanding the world 4. The understanding of the planetary interior is deepening 3. The computer is learning to predict new materials 2. It is already possible to predict crystal structures1. Structure defines properties
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

The essence of the search for the most stable structure comes down to calculating the state of matter that 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 the simplified Schrödinger equation. This is how the USPEX algorithm uses density functional theory, which 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 with an electron density, while remaining formally accurate (but in reality, approximations are inevitable). In practice, this leads to a reduction in the complexity of calculations and, as a consequence, the time 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 search for structures with the lowest energy by brute force: randomly placing atoms relative to each other and analyzing each such state. But since the number of options is huge (even if there are only 10 atoms, there will be about 100 billion possibilities for their arrangement relative to each other), the calculation would take too much time. Therefore, scientists were able 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 is calculated. The system removes the options with the highest energy, that is, the least stable, and generates similar ones from the most stable ones and calculates them. At the same time, the computer continues to randomly generate new structures to maintain population diversity, which is an essential condition for successful evolution.

Thus, logic taken from biology helped 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 parameters. 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 quite 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, whereas previous algorithms could not cope with even ten.

One of the new tasks set for USPEX at MIPT is predicting the tertiary structure of proteins from their amino acid sequence. This problem of modern molecular biology is one of the key ones. In general, scientists face a very difficult task 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 approximately 40 amino acids long.

Video 2. Polymers and biopolymers. What substances are polymers? What is the structure of the polymer? How common is the use of polymer 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 do not have the 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 with numbers, but with skill,” which is implemented here in the form of an evolutionary approach. Taking the bearing of their nearest neighbor, the robots meet and reproduce their own kind, placing them along the line between “their” vertices. The offspring of biorobots begin to carry out 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” who came across vertices below the average level are recalled (this is how selection is carried out) and dropped in again at random (this is how the maintenance of “genetic diversity” of the population is modeled).”

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

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

Areas of work of the laboratory: from thermoelectrics to drugs

USPEX turned out to be not only an effective algorithm, but also multifunctional. At the moment, under the leadership of Artem Oganov, many scientific works are being carried out in various areas. Some of the latest projects include 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, surface materials, Another is studying chemicals under high pressure. There is also an interesting project related to the prediction of new thermoelectric materials. Now we already know that adapting the method for predicting crystal structures that we came up with to thermoelectric problems works effectively. At the moment, we are ready for a big breakthrough, which should result in the discovery of new thermoelectric materials. It is already clear that the method we created for thermoelectrics is very powerful, the tests carried out are successful. And we are completely ready to look for new materials. We are also involved 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 task for us and a very interesting one.”

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

We are talking about a drug recently patented by Valery Roizen (Fig. 4), Anastasia Naumova and Artem Oganov, a drug that allows symptomatic treatment of multiple sclerosis. The patent is open, which will help reduce the price of the medicine. Multiple sclerosis is a chronic autoimmune disease, that is, one of those pathologies when one’s own immune system harms the host. This damages the myelin sheath of the nerve fibers, which normally performs an electrical insulating function. It is very important for the normal functioning of neurons: current flows through the outgrowths of nerve cells covered with myelin 5–10 times faster than through uncoated ones. Therefore, multiple sclerosis leads to disturbances in the functioning 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 is one of the authors of the patent for a medicine for multiple sclerosis, employee of the laboratory for computer design of materials, developing new dosage forms of medicines and 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 had already been used in the clinic, but scientists were able to improve the absorption of this medicine into the blood by changing the chemical composition. They obtained crystalline 4-aminopyridine hydrate (Fig. 5) with a stoichiometry of 1:5. In this form, the medicine itself and the method for its preparation were patented. The substance improves the release of neurotransmitters at neuromuscular synapses, which makes patients with multiple sclerosis feel better. It is worth noting that this mechanism involves treating 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 “enclose” 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 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 “habitual” carbon has its 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 first include diamond and lonsdaleite, the second - graphite, and the third - some fullerenes at low temperatures. Despite the wide variety of known forms of carbon, scientists under the leadership of Artem Oganov managed to discover a fundamentally new structure: it was previously not known that carbon can form “guest-host” complexes (Fig. 6). Employees of the Laboratory of Computer Design of Materials also took part in the work (Fig. 7).

Figure 7. Oleg Feya, graduate student at MIPT, employee of the Laboratory of Computer Design of Materials and one of the authors of the discovery of a new structure of carbon. 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”.

Host-guest interactions occur, 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 surrounding compounds. This behavior is widespread among biological molecules that bind together to form strong and large complexes that perform various functions in our body. In general, we mean connections 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 as a whole (Fig. 8). It is worth noting that in the open form of carbon, covalent bonds are formed between atoms. 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

The computer-aided materials design laboratory studies which substances will be stable at high pressures. Here is how the head of the laboratory argues for interest in such research: “We study 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 traditional rules. The knowledge gained about new compounds will lead to an understanding of what happens inside the planets. Because these unusual chemicals may emerge as very important materials in the planetary interior.” It is difficult to predict how substances will behave under high pressure: most chemical rules stop working because these conditions are so different from what we are used to. Nevertheless, we need to understand this if we want to know how the Universe works. The lion's share of the baryonic matter in the Universe is under high pressure inside planets, stars, and satellites. Surprisingly, very little is still known about its chemistry.

New chemistry, which is realized at high pressure in the Laboratory of Computer Design of Materials at MIPT, is being studied by PhD (a degree similar to Candidate of Sciences) Gabriele Saleh:

“I am a chemist and I am interested in high pressure chemistry. 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 this is 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 exciting. We started the conversation with fundamental things. But high pressures also exist in the real world. 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) - pressure-stable structure. In the insert above it is shown that along C axis polymer structures are formed. Studying the carbon-oxygen-hydrogen system under high pressure is very important for understanding how the planets work. H 2 O (water) and CH 4 (methane) are the main components of some giant planets - for example Neptune and Uranus, where pressure can reach hundreds of GPa. Large icy satellites (Ganymede, Callisto, Titan) and comets also contain water, methane and carbon dioxide, which are subject to pressures of 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 discover a direct application to the knowledge you gained. For example, we recently submitted a paper for publication in which we describe the results of a search for all stable compounds produced from carbon, hydrogen and oxygen at high pressure. We 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 astrophysics literature and discovered that the moons Ganymede and Callisto [moons of Jupiter] are made 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 fundamental science and ended 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 at 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 investigated 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 there would probably 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 common table salt, NaCl. It turns out that if you can create a pressure of 350 GPa in your salt shaker, you will get new connections. In 2013, under the leadership of A.R. Oganov showed 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 substances discovered are metals. Gabriele Saleh and Artem Oganov continued the 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 halogen compounds.

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 −2 oxidation state. “Standard” chemistry prohibits this. Under such conditions, new substances can be formed, for example with the chemical formula Na 4 Cl 3.

Figure 10. Crystal structure of the common salt NaCl ( 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 under high pressure is not so simple: sodium and chlorine can form other compounds. But no one knew why. Scientists performed calculations and 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 such compounds, and came to general patterns that are characteristic of them under high pressure. In order to check whether these rules are a figment of my imagination or are still objectively correct, I predicted the structures of similar compounds - LiBr or NaBr and several more similar ones. And indeed, the general rules are followed. Briefly, I have seen that there is a trend: when you apply pressure to such compounds, they form a two-dimensional metal structure, and then a one-dimensional one. 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 using several approaches to analyze chemical bonds. Also, during the work, I looked for special literature to understand whether anyone had already observed such patterns. And it turned out that yes, they did. If I'm not mistaken, sodium bismuthate and some other compounds follow the rules described. Of course, this is just the beginning. When the next papers on the topic are published, we will know whether our model has real predictive power. Because that's exactly what we're looking for. We want to describe chemical laws that would also hold 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 nobody 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 investigated this compounds and I find some rule to rationalize what is going on. I investigated how electrons 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 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 see 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. 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, do it selectively

Despite the fact that the USPEX algorithm has great predictive power within its tasks, the theory always requires experimental verification. The Laboratory of Computer-Aided Materials Design is theoretical, as even its name suggests. Therefore, experiments are carried out in collaboration 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 we often collaborate with people who do this. 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 work carried out under the leadership of Artem Oganov were published. In the article, the scientists described a new form of Na, in which it is a transparent nonmetal, 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 a dielectric appear. A pressure of 2 million atmospheres makes sodium red, and a pressure of 3 million makes it colorless.

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

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

Figure 14. Photographs of the Na sample obtained under 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 passion!

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

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

Ma Y., Eremets M., Oganov A.R., Xie Y., Trojan I., Medvedev S. et al. (2009). Transparent sodium dense. Nature. 458 , 182–185;

Lyakhov A. O., Oganov A. R., Stokes H. T., Zhu Q. (2013). New developments in evolutionary structure prediction algorithm USPEX. Comput. Phys. Commun. 184 , 1172–1182.

We publish the text of a lecture given by a professor at the State University of New York, an adjunct professor at Moscow State University, and an honorary professor at Guilin UniversityArtem Oganov 8 September 2012 as part of the series of “Public lectures “Polit.ru” at the open-air book festival BookMarket in the Muzeon art park.

"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. I am honored to give this lecture; I hope you find it interesting.

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 great extent on new materials, new technologies require new materials, materials with unique, special properties. And a story will be told about how these new materials can be developed not in a laboratory, but on a computer.

The lecture is called: “Computer design of new materials: dream or reality?” If this were completely 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 implemented, the lecture would also have no meaning, because new types 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 the dream - what is impossible, what we dream about in our leisure time - and reality, this is not yet a completely completed area, it is an area that is being developed right now. And this area will make it possible in the near future to deviate from the traditional method of discovering new materials, the laboratory one, and begin computer-aided design of materials; this would be cheaper, faster, and in many ways even more reliable. But I’ll tell you how to do it. This is directly related to the problem of prediction, forecasting the structure of a substance, because the structure of a substance determines its properties. The different structure of the same substance, say carbon, determines super-hard diamond and super-soft graphite. Structure in this case is everything. 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. For a very long time, since ancient times, people have hypothesized that matter consists of atoms. 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 Cara. And the first mention of how matter is structured, how this matter consists of these discrete particles, atoms, belongs to Johannes Kepler, a 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 to it in many aspects. But, nevertheless, the hypothesis about the atomic structure of matter remained a hypothesis until the 20th century, until a hundred years ago this hypothesis first became scientifically proven. It became proven with the help of my science, crystallography, a relatively new science that was born in the mid-17th century, 1669 is the official date of birth of the science of crystallography, and it was created by the wonderful Danish scientist Nicholas Stenon. Actually, his name was Niels Stensen, he was Danish, his Latinized name was Nicholas Stenon. He founded not only crystallography, but a number of scientific disciplines, and he formulated the first law of crystallography. Since that time, crystallography began its development along an accelerating trajectory.

Nikolai Stenon had a unique biography. He not only became the founder of several sciences, but was also canonized by the Catholic Church. The greatest German poet, Goethe, was also a crystallographer. And Goethe has a quote 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 as 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 that he gave somewhere in the Baden resorts 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 indeed a rather useless science, really at the level of some kind of mathematical charades and puzzles. But time passed, and 100 years ago crystallography emerged from the category of such sciences in itself and became an extremely useful science. This was preceded by a great tragedy.

I repeat, the atomic structure of matter remained a hypothesis until 1912. The great Austrian physicist Ludwig Boltzmann based 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, under the influence of this criticism, as well as poor health, committed suicide in 1906. He hanged himself while on vacation with his family in Italy. Just 6 years later, the atomic structure of matter was proven. So if he had been just 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 kind of experiments were these? These experiments were done by Max von Laue, or more precisely, by his graduate students. Max von Laue did not do any such experiments himself, but the idea was his. The idea was that if matter really consists of atoms, if indeed, as Kepler assumed, the atoms are built in a crystal in a periodic, regular way, then an interesting phenomenon should be observed. Not long before, X-rays were discovered. Physicists by that time had already well understood that if the wavelength of radiation is comparable to the periodicity length - the characteristic length of an object, in this case a 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 at very 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 must be similar to the size of atoms; if atoms existed, estimates of the size of the atoms were necessary. Thus, if the atomic hypothesis of the structure of matter is correct, then diffraction of X-rays from crystals should be observed. What could be easier than checking?

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

Look. Here is a laser pointer, we shine it - and what happens here? We do not use X-rays, but an optical laser. And this is not the structure of the crystal, but its image, inflated by 10 thousand times: but the laser wavelength is 10 thousand times greater than the wavelength of X-ray radiation, and thus the diffraction condition is again satisfied - the wavelength is comparable to the period of the crystal lattice. Let's look at an object that has no regular structure, a liquid. Here, Oleg, hold this picture, and I will shine the laser, come closer, the picture will be small, since we cannot project... look, you see a ring here, inside there is a point that characterizes the direct passage of the beam. But the ring is diffraction from the disorganized structure of the liquid. If we have a crystal in front of us, then the picture will be completely different. You see, we have many 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 picture. This picture is very symmetrical, and that's important. Let's applaud Oleg for a brilliant experiment that would have earned him a Nobel Prize 100 years ago.

Then, the next year, father and son Braggy learned to decipher diffraction images and determine 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 very, very complex structures based on experiment. This is the experiment that Oleg and I reproduced. Here is the initial structure, here are benzene molecules, and this is the diffraction pattern Oleg observed. 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 awarded 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 using X-ray diffraction, that great crystallographic technique.

So, we know the different states of matter: ordered crystalline and quasicrystalline, amorphous (disordered solid state), as well as liquid, gaseous and various polymer states of matter. Knowing the structure of a substance, 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 positions of the atoms. And this substance is quite important, it makes up 40% of the volume of our planet. This is the most common material on Earth. And it is possible to understand the properties of this substance, which exists at great depths, by 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 a substance so that you can 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 do not sink, we know that ice is always on the surface of the river, and not at the bottom. What's the matter? It's about the 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 occurs. I'll show you a short film, watch carefully. Melting will start from the surfaces, this is 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 regularity of the structure is lost.

Ice has several different shapes, and a very interesting form of ice is the one that results when you fill the voids in the ice structure with guest molecules. But the structure itself will also change. I'm talking about 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 - a natural gas, maybe carbon dioxide, maybe, 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 traditional 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 a practically 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 low pressure into the ice and dump it on the seabed. This ice exists there quite calmly for many thousands of years. Xenon hydrate served as an 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 low pressure, the person ceases to feel pain. It was, and appears to still be, sometimes used for anesthesia in surgical operations. Why?

Xenon, under low pressure, forms compounds with water molecules, forming the very gas hydrates that block 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 exactly this 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 the separation of molecules during oil cracking. For example, the molecules of octane and meso-octane are perfectly separated by zeolites: they are the same chemical formula, but the structure of the molecules is slightly different: one of them is long and thin, the second is short and thick. And the one that is thin passes through the voids of the structure, and the one that is thick is eliminated, and therefore such structures, such substances are called molecular sieves. These molecular sieves are used to purify water, in particular, the water we drink in our taps must pass through multiple filtration, including with the help of zeolites. In this way, you can get rid of contamination with a wide variety of chemical pollutants. Chemical pollutants are sometimes extremely dangerous. History knows examples of how heavy metal poisoning has led to very sad historical examples.

Apparently, the first emperor of China, Qin Shi Huang, and Ivan the Terrible were victims of mercury poisoning, and the so-called mad hatter's disease has been very well studied; in the 18th and 19th centuries in England, a whole class of people working in the hat industry fell ill with a strange disease very early a neurological disease called mad hatter's disease. Their speech became incoherent, their actions became meaningless, their limbs trembled uncontrollably, and they fell into dementia and madness. Their bodies were constantly in contact with mercury as they soaked these hats in solutions of mercury salts, which entered their bodies and affected the nervous system. Ivan the Terrible was a very progressive, good king until 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 severely deformed and 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 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, the first 12 years of which he was a puppet in the hands of his mother, the regent, his story is similar to the story of Hamlet. His mother and her lover killed his father, and then tried to get rid of him, it’s 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, he united China, he united weights, money, unified Chinese writing, he built the Great Wall of China, he built 6 5 thousand 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 from some strange form of manic madness. 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 the age of 50, 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 water supply, an aqueduct, and it is known that with lead poisoning, certain parts of the brain shrink, you can even see this on tomographic images, intelligence drops, IQ drops, a person becomes very aggressive . Lead poisoning is still a big problem in many cities and countries. To get rid of these kinds of unwanted consequences, we need to develop new materials to clean up the environment.

An interesting material that is not fully explained is superconductors. Superconductivity was also discovered 100 years ago. This phenomenon is largely exotic; it was discovered by chance. They simply cooled mercury in liquid helium, measured the electrical resistance, it turned out that it dropped 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 used quite widely in high-tech applications. The type of superconductivity that was discovered 100 years ago was explained, it took half a century to explain, and 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. Superconductors have many applications. For example, the most powerful magnetic fields are created with the help of superconductors, and this is used in magnetic resonance imaging. Magnetic levitating trains are another application, and here is a photograph that I personally took in Shanghai on such a train - the speed indicator at 431 kilometers per hour is visible. Superconductors are sometimes very exotic: organic superconductors, that is, carbon-based superconductors, have been known for a little over 30 years; 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 an interesting historical parallel about how the properties of materials or ignorance of them can have fatal consequences. Two stories that are very beautiful, but, apparently, historically incorrect, but I will still tell them, because a beautiful story is sometimes better than a true story. In popular science literature, it is actually very common to find references to how the effect of the tin plague - and here is a sample of it - destroyed 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 the “tin plague” - the tin simply crumbles into dust. Here is a story that I have never seen fully explained. Napoleon comes to Russia with an army of 620 thousand, fights only a few relatively small battles - and only 150 thousand people reach Borodino. 620 arrive, 150 thousand reach Borodino almost without a fight. Under Borodino there were about 40 thousand more victims, then a retreat from Moscow - and 5 thousand reached Paris alive. By the way, the retreat was also almost without a fight. What is going on? How can you go from 620 thousand to 5 thousand without a fight? There are historians who claim that the tin plague is to blame for everything: the buttons on the soldiers’ uniforms were made of tin, the tin crumbled as soon as the cold weather set in, and the soldiers found themselves virtually naked in the Russian frost. The problem is that the buttons were made from dirty tin, which is resistant to the tin plague.

Very often you can see in the popular science press a mention that Captain Scott, according to various versions, 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 Captain Scott’s diaries - he didn’t mention any airplanes, he had some kind of snowmobile, but again he doesn’t write about the fuel tank, and he doesn’t 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 in any case useful if you are going to a cold climate.

Here's a different experience, and here I need boiling water. Another effect associated with materials and their structure, which would not have occurred to any person, is the shape memory effect, also discovered completely by accident. In this illustration you see that my colleagues made two letters from this wire: T U, Technical University, they hardened this form at high temperatures. If you harden a shape at a high temperature, the material will remember that 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 just broke this shape, but if you put it in hot water, the shape is restored. And all this happens thanks 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 arise. Just 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 airplanes to reduce noise, adhesions in gas and oil pipelines. Now I need another volunteer... please, what's your name? Vika? We'll need Vicki's help with this wire, it's a shape memory wire. The same nitinol alloy, an alloy of nickel and titanium. This wire was hardened into a straight wire form, and it 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 any knots: the knot won’t unravel. And now dip it in boiling water, and the wire will remember this shape... well, has it 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 how beautiful the effect is. Let's applaud Vika. It would be great if we learned to 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 a crystal at some inscription, the inscription will always be slightly double. But, as a rule, it is indistinguishable to our eyes. In some crystals this effect is so strong that you can actually see two inscriptions.

Question from the audience: Did you say at different speeds?

Artem Oganov: Yes, the speed of light is constant only in a vacuum. In condensed media it is lower. Further, we are accustomed to thinking that each material has a certain color. Ruby is red, sapphire is blue, but it turns out that color can also depend on direction. In general, one of the main characteristics of a crystal is anisotropy - the dependence of properties on direction. The properties in this direction and in this direction are different. Here is the mineral cordierite, whose color changes in different directions from brownish-yellow to blue, this is the same crystal. Does anyone not believe me? I brought a cordierite crystal specifically so that, please... look, what color?

Question from the audience: It seems white, but like this...

Artem Oganov: From some light, like white, to purple, you just rotate the crystal. There is actually an Icelandic legend about how the Vikings discovered America. And many historians see in this legend 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 he was able 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 the sun stone is what Vika is holding 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 the twilight light, 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: daylight and electric. And finally, another interesting effect that scientists and art historians could not understand for many centuries. The Lycurgus Cup is an object that was made by Roman artisans more than 2 thousand years ago. In diffuse light, this bowl is green, and in transmitted light it is red. And we managed to understand this literally a few years ago. It turned out that the bowl was not made of pure glass, but contained gold nanoparticles, which created this effect. Now we understand the nature of color - color is associated with certain absorption ranges, with the electronic structure of a substance, and this, in turn, is associated with the atomic structure of a substance.

Question from the audience: Can the concepts “reflected” and “transmitted” be clarified?

Artem Oganov: Can! By the way, I note that these same absorption spectra determine why cordierite has different colors in different directions. The fact is that the structure of the crystal itself - 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 when light passes through the crystal, part of this range is absorbed. For example, a crystal can absorb blue light, and you can see what will happen as a result from this table. If you absorb blue rays, the output will be orange, so when you see something orange, you know that it absorbs in the blue range. Scattered light is when you have the same cup of Lycurgus on the table, light falls, and part of this light scatters and hits your eyes. Light scattering obeys completely different laws and, in particular, depends on the grain size of the object. Thanks 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. We will briefly consider now how to predict the crystal structure. This means that the problem of predicting crystal structures was considered unsolvable until very recently. This problem itself is formulated as follows: how to find the arrangement of atoms that gives maximum stability - that is, the lowest energy? How to do it? You can, of course, go through 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 time to go through them; in fact, even for fairly simple systems, say, with 20 atoms, you will need more than time life of the Universe in order to sort through all these possible combinations on a computer. Therefore, it was believed that this problem was unsolvable. Nevertheless, this problem was solved using several methods, and the most effective method, although this may sound immodest, was developed by my group. The method is called “Success”, “USPEX”, evolutionary method, evolutionary algorithm, the essence of which I will try to explain to you now. The problem is equivalent to finding the global maximum on some multidimensional surface - for simplicity, let's 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, using kangaroos, fairly unintelligent animals, you need to determine the highest point on the surface of the Earth. The kangaroo only understands simple instructions - go up, go down. In the evolutionary algorithm, we drop a group of kangaroos, randomly, to different points on the planet and give each of them instructions: 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 reach high are eliminated and shot back. A hunter comes, I almost said, an artist, a hunter comes and shoots, and those who survived get the right to reproduce. And thanks to this, it is possible to identify the most promising areas from the entire search space. And step by step, by shooting higher and higher kangaroos, you will move the kangaroo population to a global maximum. Kangaroos will produce more and more successful offspring, hunters will shoot kangaroos that climb higher and higher, and thus this population can simply be driven to Everest.

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

The most difficult thing is how to produce offspring 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 tried to make children from three, and from four. But, as it turns out, this does not lead to anything good, just like in life. A child is better off if he has two parents. One parent, by the way, also works, two parents are optimal, but three or four do not work anymore. The evolutionary method has several interesting features, which, by the way, are similar to biological evolution. We see how, from the unadapted, random structures with which we begin the calculation, highly organized, highly ordered solutions emerge in the course of the calculation. We see that calculations are most effective when the population of structures is most diverse. The most stable and most surviving populations are populations of diversity. For example, what I like about Russia is that there are more than 150 peoples in Russia. There are fair-haired people, there are dark-haired people, 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 evolution calculations.

Can we predict that the stable form of carbon at atmospheric pressures is graphite? Yes. This calculation is very fast. But besides graphite, we produce several interesting slightly less stable solutions in the same calculation. And these solutions may also be interesting. If we increase the pressure, graphite is no longer stable. And diamond is stable, and we can find this very easily too. 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, this structure. While diamonds have hexagonal rings, 5- and 7-gonal rings are visible here. This structure is only slightly inferior in stability to diamond, and at first we thought it was a curiosity, but then it turned out that this is a new, actually existing form of carbon, which was recently discovered 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.

We and our colleagues have done a lot using this method; here is a small selection of different discoveries. Let me talk about just a few of them.

Using this method, you can replace laboratory discovery of materials with computer discovery. In the laboratory discovery of materials, Edison was the unsurpassed champion, who said: “I have not suffered 10 thousand failures, I have only found 10 thousand ways that do not work.” This tells you how many attempts and unsuccessful attempts you need to make before making a real discovery using this method, and with the help of computer design you can achieve success in 1 attempt out of 1, in 100 out of 100, in 10 thousand out of 10 thousand, this is ours the goal is to replace the Edisonian 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. Almaz is a record holder in many respects. A cubic centimeter of diamond contains more atoms than a cubic centimeter of any other substance. Diamond holds the record for hardness, and it is also the least compressible substance known. Can these records be broken? Now we can ask the computer this question, and the computer will give an 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 a 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 this mean? A diamond's refractive index gives a diamond its unrivaled brilliance and internal reflection of light - and the dispersion of light means that white light will be split into the red to violet spectrum even more than a diamond does. By the way, a material that often replaces diamond in the jewelry industry is cubic zirconium dioxide, cubic zirconia. It is superior to diamond in light dispersion, but, unfortunately, inferior to diamond in brilliance. And new forms of carbon will beat diamond in both respects. What about hardness? Until 2003, it was believed that hardness was a property that people would 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 professor degree, and there I visited the founder of this whole theory. We were able to develop this theory.

Here is a table that shows how the calculated hardness determinations 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 false. We were able to understand and fix this error. And now, using this model, we can reliably predict the hardness of any substance, and we can ask the computer the following question: which substance is the hardest? 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 of carbon? The answer was discouraging: diamond, and there could be nothing harder in carbon. But you can find carbon structures that are 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. In 2001, Dubrovinsky proposed in the literature an ultra-hard substance - titanium dioxide; it was believed that in terms of hardness it was not much inferior to diamond, but there were doubts. The experiment was quite controversial. Almost all experimental measurements from that work were sooner or later refuted: 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 measured erroneously 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 achieved high accuracy.

There is another story connected with carbon that I would like to tell you - it has unfolded especially rapidly in the last 6 years. But it began 50 years ago, when American researchers conducted the following experiment: they took graphite and compressed it to a pressure of about 150-200 thousand atmospheres. If graphite is compressed at high temperatures, it should turn into diamond, the most stable form of carbon at high pressures - this is how diamond is synthesized. If you do this experiment at room temperature, then diamond cannot form. Why? Because the restructuring required to transform graphite into diamond is too great, the structures are too dissimilar, and the energy barrier that must 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 least high barrier to formation. 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 “moocarbon-shmoocarbon.” It turned out that this structure fully describes the results of that experiment 50 years ago, and the experiment 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 super-hard non-metal: an absolutely fantastic transformation! But this is not a diamond, its properties are not consistent with diamond, and our then hypothetical structure fully described the properties of this substance. We were extremely happy, wrote an article and published it in the prestigious journal Physical Review Letters, and rested on our laurels for exactly a 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 were of low resolution, and many other structures fit them. Another six months passed, a Chinese man surnamed Wang proposed W-carbon, and W-carbon also explained the experimental data. Soon the story became grotesque - new Chinese groups joined it, and the Chinese love to produce, and they churned out 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 - the alphabet is already missing. So who's right? Generally speaking, at first our M-carbon had exactly the same rights to claim rightness 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 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 only be one winner. There can only be one champion - but who exactly? You can do a high-resolution experiment, but people tried for 50 years and no one succeeded, all the results were of poor quality. You can do the calculation. And in the calculation one could 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 much you try, there will still be some Chinese who will say: I have another 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 calculating activation barriers is very, very difficult in solid-state transformations; this is a task that is extremely non-trivial; 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 spread into the embryo and further. And modeling this embryo is an extremely difficult task. But we found such a method, a method that had been 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, the initial state is strictly defined, and the final state is vaguely defined - any tetrahedral, sp3-hybridized form of carbon (and these are the states we expect under pressure), then which of the barriers will be the minimum? This method can count barriers and find the minimum barrier, but if we define the final state as an ensemble of different structures, then we can solve the problem completely. We started the calculation with the path of the graphite-diamond transformation as a “seed”; we know that this transformation is not observed in experiment, but we were interested in what the calculation would do with this transformation. We waited a little (in fact, this calculation took six months on a supercomputer) - and the calculation gave us M-carbon instead of diamond.

In general, I must say, I am an extremely lucky person, I had a 1/40 chance of winning, because there were about 40 structures that had an equal chance of winning, but I pulled out the lottery ticket again. Our M-carbon won, we published our results in the prestigious new journal Scientific Reports - a new journal of the Nature group, and a month after we published our theoretical results, the same journal published the results of a high-resolution experiment for the first time in 50 years received. Researchers from Yale University 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 carbon forms there is another experimentally and theoretically established allotrope of carbon, M-carbon.

Let me mention one more alchemical transformation. Under pressure, all substances are expected to turn into metal, sooner or later any substance will become a metal. What will happen to a substance that is initially already 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 the limiting 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, it will conduct electricity in only one direction. At higher pressures, we predicted that sodium would lose its metallicity altogether and turn into a reddish transparent dielectric, and that if the pressure was increased even more, it would become colorless, like glass. So - you take a silver metal, squeeze it - first it turns into a bad metal, black as coal, squeeze further - it turns into a reddish transparent crystal, outwardly reminiscent of a ruby, and then becomes white, like glass. We predicted this, and the journal Nature, where we submitted it, refused to publish it. The editor returned the text within a few days and said: we don’t believe it, it’s too exotic. We found an experimenter, Mikhail Eremets, who was ready to test this prediction - and here is the result. At a pressure of 110 Gigapascals, this is 1.1 million atmospheres, it is still a silver metal, at 1.5 million atmospheres it is a bad metal, black as coal. At 2 million atmospheres it is a transparent reddish non-metal. And already with this experiment we very easily published our results. 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) - the valence electrons, which provided sodium with metallicity, are sandwiched 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 clots of electron density, and our form of sodium is the simplest and most striking example of an electride known.

This kind of calculation 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 crust of the earth 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 study only the very, very surface of the Earth. The deepest well is the Kola superdeep well, 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. They invested huge sums in the USSR, 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 superdeep well drilled only into 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 Earth's core, which we will never reach. Convection of the Earth's molten outer core 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 is molten, it’s like a chocolate candy with melted chocolate, and inside is a nut - this is how you can imagine the core of the Earth. Convection of the Earth's solid mantle is very slow, its speed is about 1 centimeter per year; hotter currents go up, colder ones go down, and this is the convective movement of the Earth's mantle and is responsible for continental drift, volcanism, and earthquakes.

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

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

Pour boiling water, and I will hold Wood's alloy, and you will see how 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 Earth’s core, 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 there and there are some light trace elements, we have 5 candidates. We started with the least likely candidates - carbon and hydrogen. It must be said that until recently, few people paid attention to these candidates; both were considered unlikely. We decided to check it out. Together with Zulfiya Bazhanova, an employee of Moscow State University, we decided to take on this matter, to predict stable structures and stable compositions of iron carbides and hydrides in the conditions of the Earth’s core. We also did this for silicon, where we didn’t find any special surprises, but for carbon it turned out that those compounds that were considered stable for many decades actually 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 of the properties of the Earth's inner core perfectly, contrary to previous work. Hydrogen turned out to be a rather poor candidate; hydrogen alone cannot explain a single property of the Earth’s core. Hydrogen may be present in small quantities, but it cannot be the main trace element in the Earth's core. For hydrogen hydrides under pressure, we discovered a surprise - it turned out that there is a stable compound with a formula that contradicts school chemistry. A normal chemist will write the formula for hydrogen hydrides as FeH 2 and FeH 3; generally speaking, FeH also appears under pressure, and they have come to terms with this - but the fact that FeH 4 can appear under pressure was a real surprise. If our children write the formula FeH 4 at school, I guarantee that they will get a bad grade in chemistry, most likely even in the quarter. But it turns out that under pressure the rules of chemistry are violated - and such exotic compounds arise. But, as I already said, iron hydrides are unlikely to be important for the interior of the Earth; hydrogen is unlikely to be present there in significant quantities, but carbon is most likely present.

And finally, the last illustration is about the Earth’s mantle, or rather, about the boundary 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 this so? For a long time it was not possible to 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 is immediately clear that this structure looks completely different in different directions, and its properties should 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. It was even possible to make several predictions.

In particular, smaller planets such as Mercury and Mars will not have a layer like the D layer.” There is not enough pressure there 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, but was born in the early phase of the development of our planet. And all this can be understood thanks to predictions of new structures of crystalline substances.

Reply from the audience: Thanks to the genetic algorithm.

Artem Oganov: Yes, although this latest 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 haven’t done anything else.

Artem Oganov: This algorithm was created by me and my graduate student in 2006. By the way, calling it “genetic” is incorrect; a more correct name is “evolutionary.” Evolutionary algorithms appeared in the 70s, and they have found application in many fields of technology and science. For example, cars, ships and planes - they are optimized using evolutionary algorithms. But for each new problem 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 mathematics? It's genetics.

Artem Oganov: This is not genetics - this is mathematics. And for each new problem you need to invent your new algorithm from scratch. And people before us actually tried to invent evolutionary algorithms and adapt them to predict crystal structures. But they took algorithms from other fields 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—predicting crystal structures has required quite a lot of effort to create a working method.

All of these examples that I gave you show how understanding the structure of matter and the ability to predict the structure of matter leads 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 problems on a computer using these methods. My colleagues and more than 1000 users of our method in different parts of the world made a huge contribution to the development of this method and its application. Let me sincerely thank all these people and the organizers of this lecture, and you for your attention.

Discussion of the lecture

Boris Dolgin: Thanks a lot! Thank you very much, Artyom, 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 new material will appear for his lecture here, here , because it must be said that some of what was heard today actually did not exist at the time of the previous lectures, so it makes sense.

Question from the audience: Please tell me how to ensure room temperature at such high pressure? Any system of plastic deformation is accompanied by heat release. Unfortunately, you didn't mention this.

Artem Oganov: The point is that it all depends on how quickly you perform the compression. 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 perform 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 audience: And did your installation allow 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 compressed between two small diamonds. In such experiments, the sample has so much time to reach thermal equilibrium that the question does not arise.

Artem Oganov, one of the most cited theoretical mineralogists in the world, told us about a computer prediction that recently became 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, they managed to get closer to this dream and make it a reality.

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

Artem Oganov: “Experimenters go to the laboratory. Mix different substances at different temperatures and pressures. Get new substances. Their properties are measured. As a rule, these substances are of no interest and are rejected. And experimenters are trying again to obtain 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 also money. This process can take years. It may turn out to be a dead end and never lead to the discovery of the necessary material. But even when it leads to success, this success comes at a very high price.”

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

Prediction technology

The main thing that needs to be predicted 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 is the crystal structure. It is thanks to it that one substance is super-hard, the other is super-soft. One is a conductor of almost metal. The other is a dielectric.”

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

“In this approach, we are not trying to try out all the infinite variety of crystal structures. We will try it step by step, starting with a small random sample, within which we rank the possible solutions, discarding the worst ones. And from the best ones we produce subsidiary variants. Daughter variants are produced through various mutations or through recombination - through heredity, where from two parents we combine different structural features of the composition. From this comes a daughter structure—a daughter material, a daughter chemical composition, a daughter structure. These subsidiary compounds are then also evaluated. For example, by stability or by the chemical or physical property that interests you. And we discard those that were ranked unprofitable. Those that show promise are given the right to produce offspring. 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 the same way as Darwin’s theory of evolution; Oganov and his colleagues implement this principle on a computer when searching for crystal structures that are optimal from the point of view of a given property or stability.

“I can also say (but this is already a little on the verge of hooliganism) that when we were developing this method (by the way, the development continues. It was improved more and more), we experimented with different methods of evolution. For example, we tried to produce one child not from two parents, but from three or four. It turned out that, just like 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 optimal both in nature and on a computer.”

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

Diamond problem

It is believed that diamond, being the record holder for hardness, 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 at high temperatures it burns. In general, the search for a material that would be harder than diamond has worried humanity for many decades.

“A simple computer calculation that was carried out by my group shows that such material cannot exist. In fact, the only thing harder than diamond can be 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 super-capacitors for storing electrical energy, as well as for the further miniaturization of computer microprocessors.
“This miniaturization actually faces obstacles. Because existing dielectric materials withstand electrical charges quite poorly. They are leaking. And further miniaturization is impossible. If we can get a material that adheres 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 made quite serious progress in this direction as well.”

And the last thing Oganov does is the development of new drugs, that is, also their prediction. 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 substance of the crystal itself. The structure is also very often radically different. And we discovered 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, it is known that asbestos, which is extremely inert, is a carcinogenic substance. 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 conditions under which the formation of this kind of particles could be avoided. That is, there is hope to even find therapy and prevention of lung cancer. In this case, we are talking only about lung cancer. And in a completely unexpected way, the results of our research made it possible to understand, and maybe even prevent or cure lung cancer.”

To summarize, prediction of crystal structures can play a key role in the design of materials for both microelectronics and pharmaceuticals. In general, this 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