The use of scaled STO basis sets in SCF calculations on H– and Li+

Abstract

LCAO SCF calculations on H^– and Li⁺ have been made using uniformly scaled STO basis sets taken in either even-tempered or Clementi–Roetti forms. As in the earlier work on helium, the total energy profiles, as a function of the scaling parameter, show several minima at which the calculated electronic properties are very close in value to their Hartree–Fock counterparts. The global minimum moves towards smaller values of the optimum scaling parameter as the atomic number decreases. The least sensitive expectation values correspond to the energy of the occupied atomic orbital and 〈δ(r₁₂)〉. In contrast, the energies of the unoccupied atomic orbitals decrease monotonically towards definite limiting values as the optimum value of the scaling parameter ranges from largest to smallest values. For He and H^–, all unoccupied orbital energies decrease towards zero, whilst for Li⁺ the limiting energies are all different and negative and the number of such bound orbitals increases with the size of the basis set. The limiting energy of the lowest unoccupied orbital in Li⁺ corresponds to the energy of the occupied 2s orbital in neutral lithium. The overall pattern of the results suggests that it might be possible to select a basis set that will not only reproduce electronic properties of near-Hartree–Fock quality, but also provide a starting point for performing calculations on excited states.