Natural Energy Decomposition Analysis:  The Linear Response Electrical Self Energy

An extension of the natural energy decomposition analysis (NEDA) is described that leads to a reduced, three-component treatment of ab initio molecular interaction potentials. These components include the classical electrical (static and induced) and quantum mechanical core (σ−σ) and charge transfer (σ−σ*) interactions. The electrical component is, in turn, represented by three terms: the static interaction of unperturbed fragment charge densities, a contribution involving polarized charge densities, and an electrical self polarization energy. Extended basis set calculations demonstrate the high numerical stability of the three-component NEDA approach. Applications are presented for the Li+(H2O) and water dimer complexes. The long-range behavior of the interaction potentials of these complexes is entirely determined by the classical electrical interaction of the fragments. Core and charge transfer effects are only significant for molecular separations within roughly 1 Å of equilibrium.