Bond functions in SCF calculations on molecules containing second-row atoms

Basis set expansion in molecules containing second-row atoms by inclusion of s and p-type gaussian functions centred on the bond axes is shown to be efficient and is compared with the addition of d-orbitals to the basis set, in the test molecule SO2. Calculations on SO2 and other molecules at MBS and double-zeta level have been carried out with wave-function polarization introduced by bond functions at various locations in the molecule. Some simple rules for basis set enhancement by this method are presented.