Computer-simulation studies of anisotropic systems. Part XXIV.—Constant-pressure investigations of the smectic B phase of the Gay–Berne mesogen

Abstract

Molecular dynamics simulation studies of the smectic B phase of the Gay–Berne model mesogen at constant volume suggest that the structure of the phase may be influenced by the periodic images. To avoid this problem we have undertaken an isothermal–isobaric Monte Carlo simulation of this phase. The ability of the dimensions of the simulation box to change during the course of the simulation should allow the layered structure of the phase to be commensurate with the periodic images. The structure of the smectic B phase has been characterised using the radial distribution function, an in-plane distribution function normal to the director and the number density along the director. In addition, these distributions have been augmented with images constructed from configurations taken from the production stage of the simulation. Such images have proved to be of particular value in exploring the positions of particles in one layer relative to those in an adjacent layer; these reveal an unexpected structure for the phase. They have also allowed us to see that the layers in the smectic B phase have a slightly rippled structure. The thermodynamic properties have also been determined as a function of temperature and through the smectic B–isotropic transition. Since these results are obtained at constant pressure this facilitates comparison with the behaviour of real mesogens which are usually studied under the same condition. The agreement between simulation and experiment is found to be good.