Equilibrium behaviour of quadrupolar Kihara molecule fluids

Abstract

Perturbation theory of systems composed of the Kihara nonspherical molecules with an embedded permanent multipole moment is proposed in which the Kihara molecule fluid is taken as a reference. Properties of the reference are determined from (another) convex-molecule perturbation expansion and the reference pair distribution function is approximated by that of the corresponding Gaussian overlap fluid. The proposed method is tested by evaluating the residual energy and compressibility factor of the quadrupole Kihara fluid, with parameters corresponding to the quadrupolar two-centre Lennard-Jones (Q2cLJ) system. The simulation results of this system are used for comparison. Fair agreement is obtained. The method is employed to correlate the density and pressure along the coexistence curve of carbon dioxide. The adjusted parameters of the Kihara pair potential show great similarities with those of the Q2cLJ model used to fit the same set of experimental data; standard deviations in pressure and density differ only negligibly from those obtained for the Q2cLJ model.