A simplified approach to molecular dynamics simulations of liquid crystals with atom–atom potentials

Abstract

Molecular dynamics simulations have been performed for the nematic liquid crystal 4-n-pentyl-4′-cyanobiphenyl (5CB) using a realistic atom–atom potential as well as a pseudorealistic atom–atom potential. The latter treats the phenyl rings in the 5CB molecule as simple spheres. This method allows a considerable decrease in computational time while still retaining important aspects of the structural anisotropy. Molecular ordering has been studied using both approaches by calculating order parameters for the principle molecular axis as well as for individual molecular segments. Molecular conformations and dynamics have been examined using dihedral angle distribution functions for the biphenyl core and for the alkyl chain. Analysis of the data allows the inter and intra molecular contributions to the conformational equilibria of the chain to be separated. This information can be used to determine the conformational equilibria of the alkyl chain under the influence of the nematic field created by surrounding molecules. Transport properties have been examined by calculating diffusion coefficients in directions both parallel and perpendicular to the nematic director. All properties calculated using the pseudomolecular potential are compared with those obtained from the more complete atom–atom potential to assess the validity of the simplified approach.