AN ACCURATE INTEGRAL-EQUATION FOR MOLECULAR FLUIDS .1. HARD HOMONUCLEAR DIATOMICS

Tests of several closures for the Ornstein-Zernike equation in the case of hard spheres are considered. The best of these is extended to the case of molecular fluids and solved for a hard homonuclear diatomic fluid. Thc theory used is a modification of an earlier theory originally proposed by Verlet for the hard sphere system, which we denote as the VM theory. The results are compared with computer simulation data and with the results of the Percus-Yevick (PY) and Nonspherical Bridge Function (NSB) theories. The VM theory produces excellent results for the compressibility factor and the spherical harmonic coefficients of the pair distribution function up to a packing fraction of 0.47 and a reduced elongation of 1.0. The NSB results are not as accurate, and the PY results are less accurate still. The bridge function given by the VM, NSB, and PY closures are compared with that extracted from computer simulation pair distribution function data. The VM theory gives good agreement and is similarly superior to the NSB and PY theories.