Five types of perturbation are used in order to sample all degrees of freedom in a unit cell. Molecular perturbations include translation in a random direction and quaternion rotation around a random axis passing through the molecular center of mass. All molecular perturbations were applied to the molecule(s) in the asymmetric unit; perturbations of the other molecules in the unit cell were generated by symmetry, so as to maintain the space group symmetry. Unit cell perturbations include unit cell length changes (taking into account correlated lattice parameters in some space groups), unit cell angle changes (where allowed by space group symmetry) and unit cell volume changes. To avoid the unphysical region of the exp-6 interatomic potential, the distances between molecules were calculated after perturbation and the Monte Carlo move was rejected if any interatomic distance was shorter than the sum of covalent radii of the two elements + 0.3 Å.