Basis sets in the LCAO Xα method. On the use of bond-centered basis functions in second-row homonuclear diatomics

A series of LCAO (GTO) Xα calculations on the model system Si₂ has been performed in an attempt to establish standardized basis sets for molecules containing second-row atoms. In contrast to previous investigations, bond-centered orbital basis functions turned out to be unnecessary. The effect of bond-centered auxiliary basis functions was found to be rather minor. Spectroscopic constants for the lowest state of certain symmetries were obtained with an accuracy comparable to that of current CI investigations. Calculations on Si₂ ⁺, Al₂ and Al₂ ⁺ confirmed this finding.