Three-body symmetry-adapted perturbation theory based on Kohn-Sham description of the monomers

An implementation of three-body symmetry-adapted perturbation theory (SAPT) of intermolecular interactions based on Kohn-Sham (KS) description of monomers with dispersion and induction nonadditive energies obtained from KS frequency-dependent density susceptibilities [SAPT(DFT)] is presented. Using the density-fitting approach, the nonadditive dispersion energy can be obtained with O(N-5) scaling with respect to the system size, the best scaling among all available methods of evaluating this quantity. Numerical results are reported for the helium, argon, water, and benzene trimers. The nonadditive energy computed for these systems is in a good agreement with benchmarks. Some hybrid perturbational-supermolecular approaches are proposed that can provide-with only O(N-5) scaling-nonadditive energies with accuracy comparable to more expensive supermolecular methods, such as the third-order Moller-Plesset perturbation theory. Such approaches can be used for studying nonadditive effects in systems larger than it is currently possible with supermolecular methods at a level high enough to capture all essential components of the three-body interaction energy. (C) 2007 American Institute of Physics.