Structure, dynamics and molecular properties of liquid crystals molecules and fragments from first principles computer simulations performed on Cray T3D

We determine accurate molecular structures, dipole moments and intramolecular potentials for mesogenic fragments and liquid crystal molecules from quantum mechanical computer simulations performed on 256 nodes of a Gray T3D. We employ density functional theory and use ab initio pseudopotentials for the interaction between valence electrons and ions and the generalised gradient approximation to account for the many-body effects of exchange and correlation. Periodic boundary conditions are enforced so that the molecular electronic wavefunction can be expanded in terms of a plane wave basis set. We parameterise a torsional potential for rotation about the dihedral bond for the mesogenic fragment 2-2'difluorobiphenyl with full structural optimisation and demonstrate the influence of conformation on the molecular dipole moment. We also calculate the dipole of the nematogen 4-4' pentyl cyanobiphenyl (5CB) and various fragments.