Computer simulations of soft repulsive spherocylinders

Abstract

Computer simulations of systems of soft repulsive spherocylinders (SRS) of aspect ratio ( L = D ) equal to 4 have been carried out using the parallel molecular dynamics program GBMOLDD. At su ciently high densities the system forms stable nematic and smectic-A liquid crystalline phases. Results are presented for a series of seven isochores in the NVE ensemble, and for isobars at T ¤ˆk T ="ˆ0:5; 1:0; 1:5 in the NpT ensemble. IntroductionRecent years have seen substantial progress in the simulation of liquid crystal systems [1± 3]. Such simulations frequently require large numbers of mesogenic molecules. This is particularly true for the calculation of material properties, such as elastic constants that require the computation of a wavevector-dependen t ordering tensor in the low-k limit [4,5], or for the study of smectic phases where many particles are required to represent individual smectic layers. In these cases it is desirable to use models that are cheap, in terms of computer power, but which still capture the essential physics of real mesogenic molecules. The most commonly studied model systems are the hard spherocylinder model [6,7] and the soft-particle Gay± Berne mesogen [8± 10]. In this study, computer simulations of a`hybrid' system of soft repulsive spherocylinders (SRS), which have only been brie¯y examined in the past [11± 13], are carried out in order to determine the phase behaviour of the system. The computational model is appealing due to its relative cheapness but in this paper is shown to be rich in phase behaviour, exhibiting both the nematic and smectic liquid crystalline phases. In addition the short-range nature of this potential makes it highly suitable for use in parallel domain decomposition algorithms [14,15], which can provide for the simulation of extremely large systems [16] of mesogenic molecules.The layout of this paper is as follows: the computational model and simulation details are described in } 2, the results of our work are presented and discussed in } 3 and our conclusions are made in } 4.

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