Properties of liquid crystal molecules from first principles computer simulation

We explore the valence charge distribution, equilibrium geometry and harmonic force fields of the 4-pentyl-4'-cyanobiphenyl (5CB) molecule and the benzene (C6H6) molecule, which provides an important mesogenic fragment, using first principles techniques adapted from large scale electronic structure calculations of periodic solids. We present for the first time accurate structural data for the isolated 5CB molecule and observe subtle broken symmetries relative to the constituent mesogenic fragments. The dynamic properties of these molecules are determined by diagonalization of dynamical matrices, the elements of which are obtained directly from quantum mechanical Hellmann-Feynman forces. Results for both molecules are in excellent agreement with available spectroscopic data, and for benzene are comparable to the most accurate quantum chemistry calculations to date. For 5CB we also present values for the molecular dipole and quadrupole moments.