PERTURBATION-THEORY WITH A HARD DUMBBELL REFERENCE SYSTEM .1. APPLICATION TO LIQUID-NITROGEN

We present a perturbation theory of molecular fluids which uses an anisotropic reference assembly. At each orientation, the potential is divided according to the Weeks–Chandler–Andersen (WCA) prescription into a reference potential ε0 which contains the repulsive forces and a perturbation ε1 containing the attractive forces. To compute the properties of the reference system, a second perturbation is made about a reference system consisting of equivalent hard dumbells using the analogue of the WCA-blip function theory. The thermodynamic properties of the hard dumbell system are computed from an analytic equation of state due to Boublik and Nezbeda, and the correlation functions using a method developed by the authors. The theory is applied to a two-center Lennard–Jones model of nitrogen at high densities and shown to predict pressures in good agreement with computer simulations. © 1979, American Institute of Physics. All rights reserved.