Ab initio calculations on small hydrides including electron correlation

Abstract

Near Hartree-Fock ab initio SCF and correlation energy calculations based on the IEPA-PNO approximation are reported for F−, HF, OH−, H2O, H2F+ and H3O+ using GTO-basis sets. The SCF values for the equilibrium geometries and harmonic force constants are corrected in the desired direction by inclusion of the correlation energy. The SCF errors are, however, always overcompensated. The agreement with experiment is improved for the symmetric stretching force constants of HF and H2O, but bond lengths are nearly the same amount too long in the IEPA approximation as they are too short in the SCF calculations. In addition thereto protonation energies are computed and compared with experimental measurements.