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/cm3 at pressures about 1 GPa. Owing to the coordination number analysis, this fact can be attributed to the high content of sp1-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 sp1, sp2, sp3-bonded atoms.