Electrostatic interaction energies with overlap effects from a localized approach

An ab initio method is proposed for calculations of intermolecular forces which should be applicable to interactions of monomers containing several hundreds atoms and scale linearly with system size. This approach unifies asymptotic approximation to intermolecular forces with symmetry-adapted perturbation theory (SAPT) treatment. Inexpensive asymptotic formulas are applied to interactions of fragments of monomers which are far apart, whereas fairly expensive SAPT formulas are applied to fragments which are near each other, where overlap effects cannot be neglected. This Letter implements the method for the electrostatic interactions. The electrostatic energies are reproduced to 1% with about dozen or so atoms in near-range regions.