An Improved First-Order Perturbation Theory of Simple Fluids Using High Temperature Approximation and Random Phase Approximation

Abstract

In this paper, we have examined accuracy of an improved form of the first-order perturbation theory of simple fluids. Theory consists of the first-order perturbation theory of high temperature approximation and the random phase approximation. Inclusion of the random phase approximation enhances applicability of the perturbation theory to much wider ranges of temperatures and densities, especially to low densities. Comparisons are made between theoretical predictions and accurate computer simulation results for pressure, residual Helmholtz free energy, residual internal energy and vapor/liquid phase equilibria of Lennard-Jones fluids. In general, theoretical predictions are in very good agreement with simulation results. The random phase approximation is responsible for predicting accurate Gibbs ensemble Monte Carlo simulation results for vapor/liquid phase equilibria using the same theory in both vapor and liquid phases.