Nonempirical approximation for the ionic thermal contribution to the equations of state based on average-atom models

A simple nonempirical approximation is proposed to calculate the ionic thermal contribution to the average-atom equations of state. The approximation represents the main regularities of temperature and mass-density dependences of the ionic thermodynamic-function components revealed from the pseudoatom molecular dynamics calculations. It is shown that the employment of our approximation instead of commonly used ideal-gas or one-component-plasma approximations significantly improves the accuracy of the equations-of-state calculations done with the Liberman average-atom model.