Combination of the exact potential and multipole methods (EP/MM) for evaluation of intermolecular electrostatic interaction energies with pseudoatom representation of molecular electron densities

A new method (EP/MM) for calculation of intermolecular electrostatic interaction energies from pseudoatom expansions of molecular densities is presented. It combines numerical evaluation of the exact Coulomb integral for the short-range with the Buckingham-type multipole approximation for the long-range interatomic interactions. In first instance the method is combined with the pseudoatom representation of the atomic densities as derived from theoretical wavefunctions. The resulting electrostatic interaction energies of monomers in molecular dimers are in very good agreement with Morokuma–Ziegler decompositioning of triple-zeta DFT energies. The combination of EP/MM with densities from the theoretical databank of aspherical pseudoatoms provides more accurate results than the MMFF94 force-field at a moderate increase in computing time. EP/MM is also applicable to experimental electron densities.