Estimation of Configurational Probability and Phase Behaviour of N-n-undecyl-D-gluconamide having V-Shaped Conformation – A Molecular Simulation Approach

The present article deals with the configurational probabilities of a smectogen N-n-undecyl-Dgluconamide (GAM11). The complete neglect differential overlap (CNDO/2) method has been employed to compute the net atomic charge and atomic dipole moment components at each atomic center. The modified Rayleigh-Schr¨odinger perturbation theory along with the multicentered-multipole expansion method has been employed to evaluate the long-range intermolecular interactions, while a ‘6-exp’ potential function has been assumed for short-range interactions. The total interaction energy values obtained during different modes of molecular interactions have been used as input to calculate the configurational probability at room temperature (300 K), and smectic-isotropic transition temperature (429:7 K) using the Maxwell-Boltzmann formula. The various possible geometrical arrangements of molecular pairs have been considered. Further, an attempt has been made to explain the smectic behaviour of GAM11 in terms of their relative order based on the molecular parameters introduced in this paper

ATOMIC DIPOLE MOMENT CORRECTED HIRSHFELD POPULATION METHOD

Charge preservation is a necessary condition in population analysis. However, one such constraint is not enough to solve the arbitrariness involved in the population analysis such as Hirshfeld population. This arbitrariness results in too small Hirshfeld charges and poor reproducibility of molecular dipolar moments. In this article, the preservation of the molecular dipole moment is imposed upon the Hirshfeld population analysis as another constraint to improve the original Hirshfeld charges. In the scheme each atomic dipolar moment defined by the deformation density is expanded as contributions from all atoms in the molecule. The corresponding correction charges are then accumulated for each atom together with the original Hirshfeld charge as the predicted charge. All computed charges are generally larger than Hirshfeld charges, independent of basis set, and have very good electrostatic potential reproducibility and high correlation with the charges derived from the electrostatic potential fitting.

Molecular Ordering of a Nematic Liquid Crystal in a Dielectric Medium

A computational analysis of the molecular ordering of 4-(4'-ethoxyphenylazo) phenyl hexanoate (EPPH) has ben carried out on the basis of intermolecular interaction energy calculations. The CNDO/2 method has been employed to evaluate the net atomic charge ad atomic dipole moment components at each atomic centre of the molecule. A modified Rayleigh-Schrödinger perturbation theory alongwith 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, and corresponding probabilities have been calculated in a dielectric medium (benzene) using the Maxwell-Boltzmann formula. Further, the flexibility of various configurations has been studied in terms of variations of the probability due to departure from the most probable configuration. All possible geometrical arrangements between molecular pairs have been considered during stacking, in-plane and terminal interactions, and the most favourable configuration of the paring has been obtained. It has been observed that in a dielectric medium the probabilities are redistributed and there is a considerable rise in the prob-ability of interactions although the order of preference remains the same. An attempt has been made to explain the nematogenic behaviour of liquid crystals and thereby develop a molecular model for liquid crystallinity. Results have been discussed in the light of those obtained for other nematogens like EPPV [4-(4'-ethoxyphenylazo) phenyl valerate] and DPAB [4-4'-di-n-propoxy-azoxybenzene],