Triplet correlation functions for fluids of nonspherical molecules

Abstract

Computer simulations of orientationally averaged triplet correlation functions are presented for fluids of several nonspherical molecules. These specific models considered included hard prolate and hard oblate molecules as well as a site-site plus quadrupole representation of CO₂. A spherical harmonic expansion of the triplet function is written down and utilized in connection with an extended superposition approximation (ESA) which is based on the spherical harmonic expansions of the orientation-dependent pair correlation functions. The ESA is evaluated for the systems studied and the results are shown to be in good agreement with the directly simulated orientationally-averaged triplet function. In addition, a series representation of the functions of r ₁₂, r ₁₃, r ₂₃ (the sides of the 1, 2, 3 triangle) which had been previously suggested in connection with simulations of the triplet correlation function of spherical particles is considered here for nonspherical particles. It is shown that this approach works reasonably well, but that the number of terms needed to obtain a convergent series still remains rather large.