A computational analysis of ordering in ABCHN at the nematic-isotropic transition.

A computational analysis of ordering in the nematogenic compound 4-alkenyl bicyclohexylnitrile has been carried out based on quantum mechanics and intermolecular forces. The evaluation of atomic charge and dipole moment at each atomic center has been carried out using the complete neglect differential overlap (CNDO/2) method. Modified Rayleigh-Schrodinger perturbation theory along with a multicentered- multipole expansion method has been employed to evaluate long-range intermolecular interactions, while a '6-exp' potential function has been assumed for short-range interactions. The total interaction energy values obtained through these computations were used to calculate the probability of each configuration at room temperature (300 K), the nematic-isotropic transition temperature (364.7 K) and above transition temperature (450 K) using the Maxwell-Boltzmann formula. The various possible configurations during the different modes (i.e., stacking, in-plane and terminal) of interactions have been studied in terms of variation of probability due to small departures from the most probable configurations. An attempt has been made to analyze the characteristic features of liquid crystallinity in terms of their relative order with molecular parameters introduced in this paper.