NEWS MODELLING AND SIMULATION


Scientists refine the melting curve of graphite


Two groups of Russian physicists have used computer modelling to refine the melting curve of graphite. The findings could help improve the performance of graphene products, particularly those in high-temperature environments, such as heat shields for spacecraft. The researchers – from the Moscow


Institute of Physics and Technology (MIPT) and the Institute for High Pressure Physics of the Russian Academy of Sciences (HPPI RAS) – also found graphene ‘melting’ is in fact sublimation. The results of the study have been published in the journal Carbon. About 100 experiments have placed the


graphite melting point at temperatures between 3,000 and 7,000K. These results make it hard to determine the true value. The values returned by different computer models are at variance with each other. Associate professor Yuri Fomin, of the


Department of General Physics, MIPT, said: ‘We observed a strange “melting” behaviour of graphene, which formed linear chains. We showed it transitions from a solid directly to a gaseous state. This is called sublimation.’ The findings enable a better


understanding of phase transitions in low-dimensional materials, which are considered an important component of many technologies in development, in fields from electronics to medicine. Physicists from MIPT and HPPI RAS


compared several computer models to try and find the matching predictions. Yuri


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24 Scientific Computing World February/March 2020


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@scwmagazine | www.scientific-computing.com


Fomin and Vadim Brazhkin, from HPPI RAS, used both classical molecular dynamics and ab initio molecular dynamics. The latter accounts for quantum mechanical effects. The downside is it only deals with interactions between a small number of atoms on short time-scales. The researchers compared the results with prior experimental and theoretical data. Fomin and Brazhkin found the existing models to be highly inaccurate. But it turned out that comparing the results produced by different theoretical models and finding overlaps can provide an explanation for the experimental data. Previously, computer models predicted the melting point of graphene at 4,500


or 4,900K. Two-dimensional carbon was therefore considered to have the highest melting point in the world. The researchers produced a more


precise and unified description of how the graphite melting curve behaves, confirming a gradual structural transition in liquid carbon. Their calculations show that the melting temperature of graphene in an argon atmosphere is close to the melting temperature of graphite. The study was supported by the Russian


Science Foundation and used computing resources of the Complex for Simulation and Data Processing for Mega-Science Facilities, a federal centre of shared research facilities at Kurchatov Institute.


Miriam Doerr Martin Frommherz/Shutterstock.com


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