Fused carbon | Science and life


Solids, when heated, melt and turn into liquids, and liquids, after reaching a certain temperature, begin to boil and become vapor. This rule doesn’t always work with substances made up of large and complex molecules – for example, you are unlikely to be able to melt a piece of wood. However, for simple substances consisting of atoms of one chemical element, all three states of aggregation are usually available: solid, liquid and gaseous. If the substance is greatly cooled, it will certainly solidify, if it is strongly, strongly heated, it will become a gas, and between these extreme states there will be conditions for a liquid. But there are very few chemical elements that flatly refuse to become liquids under any circumstances, and one of them is carbon.

Despite the abundance of different forms of existence of carbon in the solid phase: and this is graphite, and diamond, and soot, and various nanotubes and fullerenes, none of these types of solid carbon can be converted into a stable liquid. The calculated melting points of carbon are so high that no known material could withstand them. Scientists, of course, go to the trick, and they sometimes succeed in melting carbon for microseconds, for example, with a laser flash or an electric discharge, but there are great difficulties in studying the properties of liquid carbon.

But if it is still not very successful to “feel” a molten diamond in reality, then this can be done at least virtually – by creating a computer model of a substance and calculating its properties. The only catch is how accurate these models will be and whether the calculated properties will be at least close to reality. The fact is that with the help of very precise quantum-chemical models it is possible to describe the interaction of only a very limited number of atoms. And when we move from a few atoms to matter, the corresponding computational task becomes unbearable even for modern supercomputers.

Therefore, in such calculations one cannot do without approximations. One of the “recipes” for creating such approximations is to take simple formulas for calculating the interaction between the atoms of a substance, but with a large set of “adjustable” coefficients. Then choose these coefficients so that our simpler formulas for relatively simple objects predict well the results obtained by more accurate and more “heavyweight” calculations. Then, it is believed that for more complex and large chemical objects, already “unbearable” for exact calculations, our simple formulas will give a result more or less similar to the truth. Or they won’t. Which also happens, so there are a large number of both the formulas themselves and the “training” models. And one of the new trends in computational chemistry has been the use of machine learning systems to build such simplified chemical models.

Approximate chemical models created using machine learning turn out to be very accurate, and most importantly, artificial intelligence can find such implicit patterns in the world of atoms and molecules that would be completely unobvious for “classical” chemists. And this opens a window, albeit still virtual, to the world of unusual and amazing substances. such as liquid carbon.

In a recent article in Carbon scientists from the Moscow Institute of Physics and Technology, MSTU im. N. E. Bauman and JIHT RAS describe the results of theoretical calculations of the properties of liquid carbon, obtained just using similar methods. As it turned out, at temperatures of 5-7 thousand degrees in liquid carbon, chains can be found that are structurally similar to carbine molecules – an extremely unstable solid phase of carbon, which chemists can synthesize only under very specific conditions.

The obtained data on the liquid phase of carbon are important not only from a practical point of view, for example, for the search for new methods for the high-temperature synthesis of carbon nanoparticles, but also for fundamental science: carbon at extreme temperatures and pressures is a frequent guest in astrophysics.

According to MIPT.

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