Accurate Intermolecular Interactions at Dramatically Reduced Cost: XPol plus SAPT with Empirical Dispersion

An efficient, monomer-based electronic structure method is introduced for computing noncovalent interactions in molecular and ionic clusters. It builds upon our explicit polarization plus symmetry-adapted perturbation theory approach, XPol+SAPT (XPS), but replaces the problematic and expensive sum-over-states dispersion terms with empirical potentials. This modification reduces the scaling from O(N-5) to O(N-3) with respect to monomer size and also facilitates the use of Kohn-Sham density functional theory (KS-DFT) as a low-cost means to capture intramolecular electron correlation. The accuracy of the resulting method [XPS(KS)+D], in conjunction with a double-zeta basis set, is superior to MP2-type methods extrapolated to the basis-set limit, with a mean unsigned error of 0.27 kcal/mol for the S66 data set. XPS(KS)+D yields accurate potential energy curves for a variety of challenging systems. As compared to traditional DFT-SAPT methods, it removes the limitation to dimers and extends SAPT-based methodology to many-body systems.