Multiple d-type basis functions for molecules containing second row atoms

Abstract

The importance of multiple sets of d functions on the energy of SO2 and other molecules of Si, P, S, and Cl has been tested by comparing total energies from the SWPS set (supplementation by five sets of d functions as recommended by Strömberg, Wahlgren, Pettersson, and Siegbahn) with those obtained with one or two sets of d functions. The energy improvement due to supplementation is very sensitive to the nature of the attached atoms and to valence shell expansion but the optimum d function exponents are not appreciably affected by either of these factors. When used in conjunction with Dunning–Hay basis sets for second row atoms, supplementation by a single set of d functions provides about 80% of the self-consistent field (SCF) energy lowering obtained with five sets; use of a second set generates about 15% more. These results are compared with the results of adding f or replacing nuclear-centered functions with bond functions. Varying d function exponents about the optimum values produces an energy surface with the same general shape for all ten molecules studied. Based on this uniformity within a limited sample of molecules containing second row elements, recommendations are presented for the inclusion of supplementary sets of d functions in basis sets and the level of energy improvement to be achieved by using them is estimated.