Approximate Hartree-Fock Calculations for the Hydrogen Fluoride Molecule

Approximate Hartree-Fock calculations have been carried out on the 1Σ+ ground state of hydrogen fluoride at three internuclear distances near equilibrium. Roothaan's method is used, with basis orbitals chosen to represent a reasonably good approximation to the atomic Hartree-Fock orbitals and to allow for the principal polarization and distortion effects that must be expected when two atoms approach to within a chemical bond distance of each other. Total energies are comparable to calculated total Hartree-Fock energies for the separated atoms, and the calculated binding energy is improved by a factor of nearly 3 over binding energy calculated with fixed atomic Hartree-Fock orbitals. Thus this improvement can be attributed to polarization and distortion effects systematically neglected in earlier LCAO calculations. Physical and spectroscopic properties of several electronic states of HF and HF+ are calculated, and are found to be in reasonable agreement with experiment. Localized ``exclusive'' self-consistent orbitals have been calculated. They give a chemical picture of the structure of the molecule and make it possible to analyse the various contributions to the dipole moment, which is mainly due to the lone pair orbitals on the fluorine atom.