Computer simulations of pure and mixed systems of disklike particles interacting with the S-function Corner potential

The S-function potential for single-site particles has been recently introduced as an extension of the Gay-Berne potential. With the S-function potential, we can model particles of other and, possibly, more realistic shapes than Gaussian overlap ellipsoids and we can simulate mixtures in a systematic manner. As an example of both applications, we have studied via Monte Carlo computer simulation assemblies of cylindrically symmetric disklike particles of two different types. They can be considered complementary perturbations of a disk, with, respectively, a depression (red-cell, R particles) and a protuberance (ufo, U particles) at the center. The former is meant to mimic the average effect of side chains of real diskotics, while the latter is a simple representation of diskotic metallomesogens. Four systems of these kind of particles have been studied as a function of temperature: two pure cases and two 1:2 binary mixtures, so that the combined effects of shape and concentration can be observed. We have found the largest variety of phases in the pure U system where also a nematic phase is present. No such phase is observed when 1/3 of the U particles are replaced by R particles, as well as in the mixture 2/3R-1/3U and in the pure R system. At the lowest temperatures investigated all systems show a lattice phase except the mixture 1/3R- 2/3U, whose organization is better described as a disordered columnar phase. (C) 2002 American Institute of Physics.