All lattice energy minimizations were performed using DMACRYS, with space group symmetry constrained throughout the optimizations. Lattice energies were assessed with a revised version of the W99 intermolecular atom-atom potential combined with a distributed multipole electrostatic model based on the molecular charge densities calculated from a distributed multipole analysis of the B3LYP/6-311G** density, with multipoles up to hexadecapole on each atom.