Vapour-liquid equilibria of stockmayer fluids

Abstract

Gibbs ensemble simulation data for Stockmayer fluids with μ*² = 3·0 and μ*² = 4·0 in the reduced temperature range of 0·77 (resp. 0·80)-0·98 and presented and compared with predictions based on the perturbation theories of Stell, G., Rasaiah, J. C., and Narang, H., 1972, Molec. Phys., 23, 393; 1974, 27, 1393. The description of the reference fluid is improved by applying the modified Benedict-Webb-Rubin equation of state instead of the Verlet-Weis implementation of the Weeks-Chandler-Andersen perturbation scheme. Second virial coefficients predicted by perturbation theory to order μ⁴ agree for Stock-mayer fluids with μ*² < 4 very well with exact values. Perturbation theory is capable of describing the low-density region of Stockmayer fluids with rather strong dipole moments. For these high values of the dipole moment, the Padé approximation of perturbation theory deviates significantly from the simulated coexistence curves in density and pressure. Compared with perturbation theory to order μ⁴, however, it is a far better approximation of the Stockmayer fluid coexistence curve. The behaviour of the Padé approximation in the critical region is not satisfactory.