The OH−(H2O)2 system: efficiency of ab initio and DFT calculations for two- and three-body interactions

Abstract

Two-body and non-additive three-body interactions in the ionic OH−(H2O)2 cluster have been studied by ab initio and DFT approaches. As the ab initio methods, the supermolecule Møller–Plesset perturbation theory (MP2, MP3, MP4SDQ, MP4), the coupled-cluster method including single, double, and approximate triple excitations [CCSD(T)], and the symmetry-adapted perturbation theory (SAPT) were used. A special attention was paid to the convergence of these treatments with respect to their perturbation operators. For the DFT calculations, the supermolecule results obtained with two functionals B3LYP and B3PW91 were examined, together with SAPT/DFT Heitler–London-type first-order terms. Various geometries of the OH−(H2O)2 trimer were considered. For some structures derived from larger clusters, the water molecules are located either in the first or in the second solvation shell. The convergence of the MP series is strongly dependent on the relative stability of the system and is especially discussed.