AN INTEGRAL-EQUATION AND MONTE-CARLO STUDY OF SQUARE-WELL FLUID MIXTURES

Square-well fluid mixtures are studied using the Ornstein-Zernike equa tion and six closure equations (PY, HNC, MSA, Martynov-Sarkisov, Verle t, and modified Verlet closures). The results for the compressibility factors and internal energies are compared with simulation data of Lee and Chao at 116 state points. At low densities all the theories consi dered give excellent thermodynamic results. In the high-density region theoretical results for the pressure are rather poor with the excepti on of the MSA pressures which remain fairly good. Radial distribution functions and thermodynamic properties have been determined by NVT Mon te Carlo simulations for several square-well mixtures. Four of these s ystems were used to test the theoretical results for the structure. Be yond the well region all the closures agree excellently with the data. Within the well, the MSA closure is the best in most cases. Several s purious solutions of the integral equations have been found at low tem peratures and intermediate to high densities.