Atomistic structure and anomalous heat capacity of low-density liquid carbon: Molecular dynamics study with machine learning potential

N Orekhov and M Logunov, CARBON, 192, 179-186 (2022).

DOI: 10.1016/j.carbon.2022.02.058

Liquid carbon remains the source of several unsolved questions related to its structure and region of thermodynamic stability. Experiments demonstrate a drastic decrease in the density for liquid carbon along the graphite melting line in the pressure range P = 1-3 GPa and the nature of this phenomenon is unclear. A recent experimental study A.M. Kondratyev and A.D. Rakhel, PRL (2019) revealed another peculiar and still unexplained feature of the liquid carbon e its excessive heat capacity. Using classical molecular dynamics with machine learning potential GAP-20, we study the structural properties of liquid carbon and demonstrate that at P < 1-2 GPa it resembles a net of sp-hybridized chains, rather than a typical covalent liquid, with nanoscale porosity of this phase being responsible for the density decrease. We also show that excessive heat capacity could be a direct manifestation of a smooth transition from a high-density sp(2)-hybridized phase into a low-density sp-hybridized. (C) 2022 Elsevier Ltd. All rights reserved.

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