Calculations of molecular ionization energies using a self-consistent-charge Hartree–Fock–Slater method

A numerical-variational method for performing self-consistent molecular calculations in the Hartree–Fock–Slater (HFS) model is presented. The molecular wavefunctions are expanded in terms of basis sets constructed from numerical HFS solutions of selected one-center atomlike problems. The binding energies and wavefunctions for the molecules are generated using a discrete variational method for a given molecular potential. In the self-consistent-charge (SCC) approximation to the complete self-consistent-field (SCF) method the results of a Mulliken population analysis of the molecular eigenfunctions are used in each iteration to produce ’’atomic’’ occupation numbers. The simplest SCC potential is then obtained from overlapping spherical atomlike charge distributions. The molecular ionization energies are calculated using the transition-state procedure; results are given for CO, H2O, H2S, AlCl, InCl, and the Ni5O surface complex. The agreement between experimental and theoretical ionization energies for the free-molecule valence levels is generally within 1 eV. The simple SCC procedure gives a reasonably good approximation to the molecular potential, as shown by comparison with experiment, and with complete SCF calculations of Baerends et al. on CO, H2O, and H2S.