Interaction energies for the water dimer by supermolecular methods and symmetry-adapted perturbation theory: the role of bond functions and convergence of basis subsets

Using a systematic series of basis sets in supermolecular and symmetry-adap ted intermolecular perturbation theory calculations it is examined how inte raction energies of various water dimer structures change upon addition and shifting of bond functions. Their addition to augmented double- and triple -zeta basis sets brings the sum of the electron correlation contributions t o the second-order interaction energy nearly to convergence, while accurate first-order electrostatic and exchange contributions require better than a ugmented quadruple-zeta quality. A scheme which combines the different pert urbation energy contributions as computed in different basis subsets perfor ms uniformly well for the various dimer structures. It yields a symmetry-ad apted perturbation theory value of -21.08 kJ/mol for the energy of interact ion of two vibrationally averaged water molecules compared to -21.29 kJ/mol when the full augmented triple-zeta basis set is used throughout.