Molecular dynamics simulation of a nematic liquid crystal

Abstract

The article describes molecular dynamics simulations of 4-n-pentyl-4′-cyanobiphenyl (5CB) in the nematic phase at 300 K using two interaction models. The first model comprises united atoms, while in the second, shorter simulation, the hydrogen atoms are explicitly included. Liquid crystalline order parameters were calculated using various definitions of molecular frames and were found to be in reasonable agreement with experiments. Distributions of dihedral angles and relative populations of various conformations in the alkyl chain have been determined. Translational and rotational diffusion processes were investigated using time correlation functions, and were compared with experimental results. Local order parameters, relevant for deuterium nuclear magnetic resonance (NMR) spectra, were determined for the segments in the alkyl chain. Proton NMR line shapes were calculated from the trajectory using an approximate method for determination of the dipole–dipole Hamiltonian matrix. These line shapes were found to be very sensitive to conformational distributions and therefore to the force field used in the simulation.