A TWO PARTICLE CLUSTER THEORY FOR UNIAXIAL NEMATIC LIQUID CRYSTALS FORMED BY BIAXIAL MOLECULES

A two-particle cluster theory is presented to study uniaxial nematic liquid crystals formed by biaxial molecules, which interact with each other via dispersion forces. The equation for the molecular orientational distribution functions in two-particle cluster approximation is obtained and is solved by an terativemethod. The temperature dependences of the order parameter and of the internal energy per particle are calculated, and the values of the relevant quantities at the nematic isotropic phase transition are given. The present theory, by taking into account the short range correlations between molecules , yields improved results compared with the mean field theory.