Molecular dynamics simulations of flexible liquid crystal molecules using a Gay-Berne/Lennard-Jones model

Molecular dynamics simulations are described for liquid crystal molecules composed of two Gay-Berne particles connected by an eight-site Lennard-Jones alkyl chain. Calculations have been carried out for 512 molecules in the NVE and NPT ensembles for simulation times of up to 6.4 ns. The system exhibits the sequence of phases: isotropic liquid, smectic-A, smectic-B, and the simulations demonstrate the spontaneous growth of a smectic-A liquid crystal over a period of approximately 6 ns on cooling from the isotropic liquid. Model molecules are seen to remain flexible and able to change conformation in the smectic-A phase. As temperature is reduced molecules become elongated as the number of gauche conformations drops, leading to a small increase in the spacing of smectic layers. The latter is seen through the temperature dependence of the Gay-Berne radial distribution function resolved parallel to the direction of orientational order. Results are presented which show an odd-even variation of orientational order parameters for bonds in the alkyl chain, and a change in effective torsional potentials as the system is cooled from isotropic liquid to a smectic-A phase. (C) 1997 American Institute of Physics. [S0021-9606(97)50444-2].