Equation of State for Molten Alkali Halides by Thermodynamic Perturbation Theory

Several variants of the equation of state (EoS) for molten alkali halides are considered using the thermodynamic perturbation theory. Most attention is focused on taking into account the charge-induced dipole (or induction) term to pressure. The model of charged hard spheres of different diameters within the mean spherical approximation is used as a reference system. The value of the extra induction contribution to the pressure is about 5–10% of the Coulomb input and, thus, leads to a better agreement between the calculation results and experimental data. It is shown that the EoS through the energy gives superior results as compared to the experimental data on molten alkali halides near their melting points. Trends in density change with the ionic radii and the polarizabilities are analyzed.