Multiphase Equation of State for Solid, Liquid, and Plasma Carbon

The multiphase equation of state (EOS) and thermodynamic properties of carbon (C) in a wide range of temperature and density are required to perform the principal shock Hugoniot calculations and hydrodynamic simulations. A parametric EOS model based on the DFT-QMD data is developed for solid (diamond, BC8, simple-cubic, simple-hexagonal) and liquid phases of C and implemented in the Radiative Emissivity and Opacity of Dense Plasmas (REODP) code [Miloshevsky et al. PRE 92 (2015) 033109]. In this model the Helmholtz free energy of each phase is decomposed into the zero-Kelvin, ion-thermal, and electron-thermal contributions that are parametrized separately for each of C phases. The REODP results on the EOS and other thermodynamic functions (enthalpy, entropy, heat capacity, isothermal compressibility, etc.) of solid and liquid phases of C are validated against the available computational and experimental data. The EOS of warm and hot dense C plasma are calculated using the first principle Hartree-Fock-Slater - Collisional-Radiative Steady-State model implemented in the REODP code. The plasma EOS is found to be in good agreement with published computational and experimental data.