Intra- and intermolecular potential energy surfaces of the 4,4'-di-n-heptyl azoxybenzene molecule have been sampled by ab initio calculations and represented through a force field suitable for classical bulk simulations. The parametrization of the molecular internal flexibility has been performed by a fitting procedure based on single molecule Hessian, gradients and torsional energies, computed using density functional theory. The intermolecular part of the force field has been derived as a pure pair potential, by fitting the dimer potential energy surface sampled by the Fragmentation Reconstruction Method. Preliminary molecular dynamics runs have been performed on systems of 210 and 600 molecules at atmospheric pressure and different temperatures, showing the presence of ordered and isotropic phases. Several properties have been computed, all resulting in a good agreement with the corresponding experimental data.