A theory of freezing for molecular liquids

Abstract

A synthesis of density functional-variational theory with statistical mechanical perturbation theory of liquids and spherical harmonics expansion is proposed to investigate the nature of freezing transitions in molecular systems. The theory is applied to hard core fluid models consisting of hard ellipsoids and hard dumbbells. For a small anisotropy of molecules the fluid freezes to an orientationally disordered lattice phase (plastic phase). For a large enough anisotropy an orientational freezing (nematic phase) occurs in the fluid of hard ellipsoids. These results are in qualitative agreement with computer simulations. At the isotropic-plastic transition we find that values of the first peak of the liquid structure factor vary with anisotropies for both hard dumbbells and hard ellipsoidal molecules. A criterion for orientational freezing is found.