Molecular ordering of Fluoro-Nematogen in a dielectric medium at phase-transition temperature: a statistical–mechanical approach based on computer simulation

Abstract

A molecular-ordering study of p-phenylene-4-methoxy benzoyl 4-trifluoromethylbenzoate (FLUORO) in a dielectric medium (benzene) has been carried out on the basis of statistical mechanics and computer simulation. The atomic net charge and atomic dipole moment at each atomic centre has been evaluated using the CNDO/2 method. The modified Rayleigh–Schrodinger perturbation theory with multicentered–multipole expansion method has been employed to evaluate the long-range intermolecular interactions, while ‘6-exp’ potential function has been assumed for the short-range interactions. The total interaction energy values obtained through these computations were used to calculate the probability of each configuration in a dielectric medium at the phase-transition temperature (506 K), using the MB-formula. The flexibility of various interacting configurations was studied in terms of variation of probability due to departure from the most probable configuration. It has been observed that in dielectric medium the energies/probabilities are redistributed, and there is considerable rise in the probability of interaction, although the order of preference remains the same. The results are discussed in the light of experimental observations.

Keywords:

• CNDO/2 method
• Interaction energy
• Quantum chemistry
• Computer simulation

Acknowledgments

The financial support rendered by 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

¹This has been defined as the ratio of probability being at maximum probable point having ± 0.2 Å displacement along the long molecular axis.

FIGURE 8 (a) Translational rigidity parameter as a function of temperature for stacking interactions; (b) translational rigidity parameter as a function of temperature for in-plane interactions.