Beyond the isotropic atom model in crystal structure prediction of rigid molecules: Atomic multipoles versus point charges

The lattice energies of predicted and known crystal structures for 50 small organic molecules with constrained (rigid) geometries have been calculated with a model potential whose electrostatic component is described by atom-centered multipoles. In comparison to previous predictions using atomic point charge electrostatics, there are important improvements in the reliability of lattice energy minimization for the prediction of crystal structures. Half of the experimentally observed crystal structures are found either to be the global minimum energy structure or to have calculated lattice energies within 0.5 kJ/mol (0.1 kcal/mol) of the global minimum. Furthermore, in 69% of cases, there are five or fewer unobserved structures with lattice energies calculated to be lower than that of the observed structure. The results are promising for the advancement of global lattice energy minimization for the ab initio prediction of crystal structures and confirm the utility of representing electrostatic contributions to the energy with atom-centered multipoles.