Optimized Cluster Expansions for Classical Fluids. III. Applications to Ionic Solutions and Simple Liquids

Abstract

In a previous paper we have derived a number of simple approximations for the thermodynamic and structural properties of liquids. Here we test these approximations by applying them to models for ionic solutions and atomic liquids and comparing the results with those obtained from Monte Carlo and molecular dynamics simulations. In particular, the pair-correlation functions for 1–1 primitive model aqueous ionic solutions are calculated using the EXP approximation. The internal energy for 2–2 salts is obtained from the ORPA+B2 approximation. The pair-correlation function for the Lennard-Jones fluid is calculated with the EXP approximation. In all cases the results obtained agree closely with those obtained from computer experiments. Thus, the ORPA+B2 approximation for the free energy and the EXP approximation for the pair correlation function provide a theory that is both very accurate and applicable to a wide variety of classical fluids.