We determine the molecular vibrational frequencies and displacement patterns for the 4-4’ pentyl-cyanobiphenyl (5CB) molecule by first principles density functional theory. All dynamic properties of the isolated molecule are obtained directly by diagonalisation of the dynamical matrix, the elements of which are determined from Helimann-Feynman Forces. Periodic boundary conditions are used which allow for the expansion of the molecular electronic wavefunction in terms of a delocalised plane wave basis set. These calculations are in excellent agreement with the results of vibrational spectroscopy and they provide a reliable means of predictive modelling of molecular properties and can be applied to as yet unsynthesised molecules.