Computer simulation studies of anisotropic systems

Abstract

We have simulated the properties of an ensemble of biaxial particles interacting via an anisotropic pair potential, truncated at the second rank terms, using the Monte Carlo technique. The particles are confined to the sites of a face centred cubic lattice and the interactions are restricted to nearest neighbours. The system exhibits three phases in addition to the biaxial crystalline phase at absolute zero. There is a rotationally disordered (isotropic) phase followed by a uniaxial rotationally ordered (nematic) phase which in turn becomes biaxial. The isotropic-nematic transition is found to be first order while the uniaxial-biaxial nematic transition is almost certainly second order. These observations confirm therefore the qualitative predictions of approximate theories of nematics formed by non-cylindrically symmetric particles. The quantitative agreement with certain of these theories for quantities, such as the order parameter and the transition temperature, is quite good.