BASIS SET SUPERPOSITION ERRORS AND COUNTERPOISE CORRECTIONS FOR SOME BASIS-SETS EVALUATED FOR A FEW X-...M DIMERS

SCF calculations of the interaction energy ΔE along the approaching path of an anion to a neutral molecule (general formula of the system considered: H2OF-) have been carried out using several basis sets (MINI-1, 4-31G, 3-21G+, 6-31G**, 6-31G**+VPS, 6-31G**+VPS(2d)S). The ΔE decomposition has been analyzed and subjected to counterpoise corrections. The last two basis sets are almost unaffected by BSSEs, whereas the others show different behaviors: the addition of diffuse functions to the 3-21G basis set produces a beneficial effect on the description of the interaction energy of the systems considered (bifurcated and linear structures of H2O⋯F- and HO-⋯HF, with the four atoms collinear). On the contrary, the addition of polarization functions to the N-31G basis sets (as in the 6-31G** one) slightly affects the trend of the curves, which are generally similar to those obtained with the 4-31G basis set. Simple approximate formulas, able to give an estimate of the interaction energy from the electrostatic energy component only, are proposed. © 1990 American Chemical Society.