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Abstract
Computer simulations of ordering in three nematogenic acids (nOCAC) having two, four, and six carbon atoms in the alkyl chain was carried out on the basis of quantum mechanics and intermolecular forces. The evaluation of atomic charges and dipole moment at each atomic center was carried out through an all-valence electron (CNDO/2) method. The configurational energy has been computed using the Rayleigh-Schrodinger perturbation method. The total interaction energy values obtained through these computations were used to calculate the probability of each configuration in a dielectric medium (i.e., noninteracting and nonmesogenic solvent, benzene) at phase transition temperature using the Maxwell-Boltzmann formula. It was observed that in dielectric medium the energies/probabilities are redistributed and there is considerable rise in the probability of interactions, although the order of preference remains the same. An attempt has been made to develop a new and interesting model of nematogenic acids in dielectric medium. The present investigation provides theoretical support to the experimental observations.
Acknowledgments
The financial support of the Department of Science & Technology (Grant No. SP/S2/M-34/2000) and the Council of Scientific & Industrial Research (Grant No. 03(0932)/01/EMR-II), New Delhi, India is gratefully acknowledged.
Notes
*Nematic → isotropic transition temperature.
A, probability in vacuum; B, probability in dielectric medium.
Average dielectric constant of benzene = 2.25.
1This has been defined as the ratio of probability being at maximum probable point having ±2 Å displacement along the long molecular axis.