∆U intra is the intramolecular energy penalty for deforming each molecule in the asymmetric unit cell from its unconstrained in vacuo conformation to its conformation in the crystal, while U inter is the intermolecular energy contribution to lattice energy. θ denotes the vector of molecular conformational variables (e.g., bond lengths, bond angles, and torsion angles). Ω relates to all other geometric variables such as the centres of mass of all molecules in the asymmetric unit cell in fractional coordinates (r 0 ), the variables defining molecule orientation (i.e., Euler angles) for each molecule in the asymmetric unit cell, and the lattice lengths and angles of the unit cell. The intermolecular energy model also depends on the empirical model parameters denoted p. For clarity in the rest of this paper, we use a semi-colon ";" to make the distinction between variables (which come before the ";") and constants (which come after the ";"), as shown in Equation ( ).