Comparison of Some Calculations on H2O and H2S

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Abstract
For the H2O and H2S molecules, a comparison is made of the values of the molecular energy, molar diamagnetic susceptibility, coherent x‐ray scattering factor, dipole moment, 〈1/r〉 and 〈1/r2〉 as calculated by different approximate treatments. The results of a united‐atom (UA) calculation, the LCAO—MO—SCF extended one‐center expansion (OCE) approach of Moccia, and the LCAO—MO—SCF minimal multicenter expansion (MCE) treatment of Ellison and Shull are compared for H2O. For H2S, UA and OCE calculations are compared. All theoretical values are compared with experiment where possible, and the relative merits of the different approximate treatments are discussed. We also discuss results which might be obtained for H2S from a minimal LCAO—MO—SCF—MCE calculation. Also for H2S, we report the results of modifications in our earlier UA approach. Although the conclusions drawn in our earlier work remain unchanged by the modifications, we note a pleasing improvement on our earlier values for the force constant, molar diamagnetic susceptibility, and molecular energy.