Each trial structure was then lattice energy minimized using the DMACRYS software to locate the nearest (downhill) local minimum on the lattice energy surface. Molecules are held rigid throughout at their DFT optimized geometries and intermolecular interactions are modelled using an empirically parametrized exp-6 repulsion-dispersion potential combined with atomic multipoles for electrostatic interactions from a distributed multipole analysis. Full details of lattice energy minimization are provided in the supporting information.