The ion equation of state of plasmas in the warm dense matter regime

The existing "quotidian equation of state (QEOS) " model [More et al., Phys. Fluids 31, 3059 (1988)] has been revised, and an alternative set of formulas is provided for the Helmholtz free energy, internal energy, heat capacity, and pressure. A novel scheme for constructing the ion equation-of-state is proposed based on the additive of solid and fluid components that act throughout the temperature range, in contrast to the QEOS that matches the thermodynamic parameters at selected interfaces. These components are continuous along with their first and second derivatives and obey limiting cases and thermodynamics laws (Lindemann melting, Dulong-Petit law, Gruneisen pressure law, and ideal gas law). Thus, the new scheme eliminates discontinuities in thermodynamics parameters across interfaces and ensures that the thermodynamics parameters are consistent with each other. The Helmholtz free energy, internal energy, heat capacity, and pressure have been approximated with computationally efficient formulas that can be used as parts of other models, e.g., hydro-simulations.