A new reference system in the variational method of thermodynamic perturbation theory

Abstract

A study was conducted to demonstrate a new reference system in the variational method of thermodynamic perturbation theory. The square-well (SW) model was considered as the reference system for conducting the investigations. The SW reference system described in two different variants of the theory of fluids was considered for conducting the investigations. These two different variants of the theory of fluids were those that were in the random-phase approximation (RPA) and in the mean spherical approximation (MSA). It was necessary to have convenient expressions for the structural factor a(q) and the entropy S of the chosen reference system for implementing the variational method. The applicability of the new reference system in two approximations (RPA and MSA) was also analyzed by the example of liquid Na at T = 373 ?.