Atomistic simulations of the equation of state and hybridization of liquid carbon at a temperature of 6000 K in the pressure range of 1–25 GPa

Abstract

The equation of state and the structure of liquid carbon are studied by molecular simulation. Both classical and quantum molecular dynamics (QMD) are used to calculate the equation of state and the distribution of chemical bonds at 6000 K in the pressure range 1-25 GPa. Our calculations and results of other authors show that liquid carbon has a fairly low density on the order of 1.2-1.35 g/cm at pressures about 1 GPa. Owing to the coordination number analysis, this fact can be attributed to the high content of sp-bonded atoms (more than 50% according to our ab initio computations). Six empirical potentials have been tested in order to describe the density dependence of pressure and structure at 6000 K. As a result, only one potential, ReaxFF/lg, was able to reproduce the QMD simulations for both the equation of state and the fraction of sp, sp, sp-bonded atoms.

Comparative study of melting of graphite and graphene

“…The results obtained in Ref. [17] at T = 6000 K are in better agreement with the results of the GAP model at T = 5000 K [8] than with other ab initio studies at the same temperature [17]. Thus, the accuracy of the DFT results are doubtful because these results obtained with different functionals differ from each other larger than the results obtained for temperatures differing by 1000 K.…”

“…Agreement between different publications is rather poor. Moreover, the best agreement is achieved between the results obtained in [17] and [19] although the simulations in the former and latter works are performed for T = 6000 and 7000 K, respectively. The situation with hybridization is very similar.…”

“…For instance, EoSs calculated in several works by ab initio molecular dynamics simulation are compared in Ref. [17]. Agreement between different publications is rather poor.…”

Simulating the structural diversity of carbon clusters across the planar-to-fullerene transition

“…Turning now to local order parameters, the hybridization state of each atom was quantified for all stable configurations R of the databases. In many computational studies that do not explicitly compute the electronic structure [78][79][80][81][82] hybridization is defined based on coordination numbers only. However, such a definition cannot account for the chemical complexity and possibly reactive atoms that are under coordinated.…”

Melting temperature of diamond and cubic boron nitride at 15 gigapascals

“…But we know the thermal expansion of graphite during melting at low pressure (about 5.4 GPa) was less than 24% [55], and the greater the pressure, the graphite expands less during melting [56]. We chose the density of liquid graphite at 15 GPa from simulation results with quantum molecular dynamics [57]; the value is 2.4 g/cm 3 . The density of solid graphite under 15 GPa was calculated from the initial density combining the Birch-Murnaghan equation [58,59].…”