Fluids of spheres containing quadrupoles and dipoles: A study using perturbation theory and Monte Carlo computations

Abstract

Thermodynamic perturbation theory is applied to fluids of hard spheres containing quadrupole moments, and the first two nonvanishing terms are calculated. Calculations are carried out to the same order for fluids containing both dipoles and parallel quadrupoles. Monte Carlo computations are performed for a range of quadrupole moments, both for the purely quadrupolar case and for the dipole–quadrupole case with fixed dipole (μ*=1.0). As in the purely dipolar case, convergence of the perturbation series is poor and two terms are inadequate. The Padé approximation to the series is again found to give a remarkably successful representation of the Monte Carlo results, although it is inexact. There is evidence that the perturbation series converges more rapidly than one would infer from the Padé formula. Quadrupoles appear to have much larger thermodynamic effects than comparable dipoles, and some interesting contrasts in their structural behaviors are discussed.