Molecular simulation of intermolecular attraction and repulsion in coexisting liquid and vapour phases

The contributions of intermolecular attraction and intermolecular repulsion to the properties of coexisting liquid and vapour phases for a Lennard-Jones fluid are determined from Gibbs ensemble simulations. Intermolecular attraction and excess intermolecular repulsion contribute almost equally to the compressibility factor. The contribution of intermolecular attraction to the configurational energy reported here is typically more than twice the contribution from excess repulsion. The simulation data are compared with calculations for the Lennard-Jones equations proposed by Hansen, Ree and Nicolas et al. The equations of Hansen and Ree incorrectly estimate the contribution of attractive and repulsive intermolecular interactions to the properties of both the liquid and vapour phases.