A set of intermolecular potential energy functions have been developed for use in computer simulations of mesogenic molecules in the isotropic and liquid crystalline phases. Primarily. the force field parameters have been developed for the mesogens GG5Cl and me5NF. Together, these molecules contain a number of important structural features present in many calamitic mesogens: including conjugated phenyl rings, lateral fluorination, an eater group, alkyl chains, terminal dipolar groups (chloro and cyano groups respectively). Where possible we have adopted data from the AMBER and OPLS-AA force fields to describe these systems, and have extended these force fields using a combination of high level quantum mechanical calculations and X-ray structural data. The potential functions obtained in this way are used to define a liquid crystal force field (LCFF) that can be extended easily to other mesogens containing different fragments. Validation of the LCFF was carried out by computing structural and thermodynamic data for the molecules me5NF. GG5Cl and the mesogenic fragments phenyl acetate and methyl benzoate using molecular dynamics simulations.