Order Parameters and Mean Field Theory for Systems of Uniaxial Molecules

A general method is developed for finding the order parameters describing the various phases of a system of anisotropic molecules. The order parameters are introduced on the basis of the expansion of the one-particle distribution function in the generalized Fourier series, and the symmetry of the intermolecular potential. The free energy of the system is considered in the Landau form. This method is applied to a system of axially symmetrical molecules with the Kobayashi interaction potential. It is found that only three Fourier components of the interaction potential are responsible for the system's behaviour. The phase diagram of the system is discussed and the possibility of the existence of a biaxial nematic phase is established.