An improved way of minimizing free energy in the variational method with the square well reference system

Abstract

For the variational method of the thermodynamic perturbation theory with the square well reference system to which the semianalytical way of solving the mean spherical approximation is applied, a new way of minimizing the free energy is proposed. The approach is applied to liquid sodium and potassium, the effective pair interaction in which is described within the framework of the pseudopotential theory. For each of the metals under study, the global minimum of the free energy was found as a function of two independent variables (the hard core diameter and the mean atomic volume). In this minimum, a better agreement between the calculation results and the experimental data is obtained than when using the hard sphere reference system.