Molecular Calculations. I. LCAO MO Self-Consistent Field Treatment of the Ground State of H2O

Abstract

A theoretical study of the ground state of the water molecule utilizing the self-consistent field molecular orbital method in the linear-combination-of-atomic-orbitals approximation is reported. All 10 electrons have been explicitly included, and all integrals have been retained in the calculations. Results are listed for six different values of the bond angle from 90 to 180 degrees, but only for the experimentally observed OH distance. The effect of inner-shell outer-shell mixing is investigated and shown to have a significant effect upon the results. The electronic configuration is discussed both from the viewpoint of molecular and equivalent orbitals. The computed dipole moment is 1.51 D. The SCF ionization potentials agree well with the experimental values, their order of assignment being quite definitely established. The calculated total electronic energy is in error by about 0.75%. This energy changes by only 0.13% for a change in bond angle from 90° to 180°, however, and consequently, the treatment leads to an incorrect value for the equilibrium bond angle. The effect of configuration interaction is considered, and some investigation is made concerning the first excited electronic state.