Monte Carlo study of induced bond orientational ordering in two-dimensional liquid-crystal models.

Abstract

The results of Monte Carlo simulations on a two-dimensional fluid of particles interacting via anisotropic van der Waals forces are reported. This nonseparable potential exhibits a nematic phase in which the ordering in the molecular director induces an ordering of the nearest-neighbor bond orientations with rectangular symmetry. To make comparison with this behavior, we have studied a separable system that also exhibits a nematic phase. Unlike the nonseparable case, we find that the separable system exhibits only short-range order in the correlations of the nearest-neighbor bond orientations. The phenomenological couplings between molecular and bond orientations present in Landau theories of liquid crystals play an important role in explaining the phase transitions observed in smectic-liquid-crystal films. Our results lead us to conclude that these couplings take their microscopic origin in the nonseparability of the intermolecular pair potential.