Hard-sphere perturbation theory for classical fluids to high densities

Abstract

This paper describes a number of developments in the very successful extension by Ree and co-workers (KLRR theory) of the Weeks, Chandler and Andersen (WCA) hard-sphere statistical perturbation theory of classical fluids to high density. The optimum break-point for the potential into a repulsive reference part of short range and a predominantly attractive long range perturbing part is found, and (a) clarifies and justifies the success of the simple KLRR prescription based on a close-packing argument, and (b) suggests a smooth density-dependent break-point to replace the two-piece KLRR prescription, thereby avoiding a discontinuity in the derivative of the effective hard-sphere diameter D. Other developments concern the evaluation of D from the implicit WCA criterion, which is re-written in a convenient pseudo-explicit form, and the evaluation of the first-order free energy for the α-exponential-6 potential.