A density functional treatment of the hard dumbbell freezing transition

Abstract

We present the first implementation of our density functional theory [J. Chem. Phys. 85, 5971, 5977 (1986)] to investigate a fluid–solid phase transition. In this theory, designed specifically for polyatomic systems, the entropy functional with bonding constraints is treated exactly, and approximations are generated by truncating expansions of the intermolecular interaction part of the free-energy density functional. We examine the theory resulting from the quadratic truncation of the interaction free energy, and determine the resulting phase diagram for hard dumbbell molecules. The results for short bond lengths are in accord with known trends from experiment and simulation. However, the theory predicts no plastic crystal transition for hard dumbbells with a bond length that might characterize nitrogen, for which the experimental β phase is a plastic crystal. Reasons for this behavior are discussed.