A modified van der Waals model for mixtures of substances has been used to construct wide-range semiempirical equations of state of liquid and gaseous argon, krypton, and xenon with allowance for vaporization and thermal ionization. The empirical functions concretizing the model have a simple form. They contain a small number of free parameters, which are adjusted so as to ensure (if possible) the best agreement with experimental data. Model calculation results have been compared to experimental data at pressures of up to ≈1000 GPa and calculation results obtained in other models at pressures above 1000 GPa. In the low-density/high-temperature limit, the model transforms into an equation of state of a mixture of ideal gases of atoms, ions of all multiplicities, and electrons with concentrations determined by the system of Saha equations.
A. B. Medvedev (Wed,) studied this question.