Phase equilibria of the two-dimensional Lennard-Jones fluid: reference systems and perturbation theories

Abstract

The gas-liquid coexistence curve of a two-dimensional Lennard-Jones system has been calculated using three different thermodynamic perturbation theories: Zwanzig (to second order), Gibbs-Bogoliubov variational method, and Weeks-Chandler-Andersen. The results of recent approximate expressions for the Helmholtz free energy and equation of state of the underlying hard disc reference system were compared also. Agreement between Gibbs ensemble Monte Carlo simulations and our calculations are fair only over a narrow range of thermodynamic states, both in the liquid and gas phases.