Near Hartree-Fock Calculations on the Ground State of the Water Molecule: Energies, Ionization Potentials, Geometry, Force Constants, and One-Electron Properties

Abstract

Near Hartree-Fock wavefunctions have been calculated for the ground state of the water molecule using both Slater and contracted Gaussian basis sets. Total energies of −76.063 hartree were obtained with a (5s4p1d/3s1p) Slater basis and a [6s5p2d/3s1p] contracted Gaussian basis derived from an (11s7p2d/5s1p) primitive set; these energies are estimated to be within 0.003±0.002 hartree of the Hartree-Fock limit. The Hartree-Fock wavefunctions account for ∼70% of the dissociation energy of water. The Hartree-Fock vertical ionization potentials (in electron volts), 11.1(2B1), 13.3(2A1), and 17.6(2B2), are too low by 1–1.5 eV as expected. With the Gaussian basis set a potential surface was computed and the equilibrium geometry and harmonic force constants were calculated. The calculated bond length, 0.941 Å, and bond angle 106.6°, are in good agreement with the experimental values, 0.957 Å and 104.52°. In spite of the rather good agreement for the geometry, the force constants are in error by 15%–20%. This is attributed to an inadequancy of the Hartree-Fock model. A number of one-electron properties were also computed; they differ only slightly from those reported in earlier work and are in satisfactory agreement with experiment. Plots of the valence (canonical) molecular orbitals are given.