Valence electron studies with Gaussian-based model potentials and Gaussian basis functions. IV. Application to molecular systems containing first row atoms

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Abstract
The previously developed simple valence−only electronic structure theory based on atomic core model potentials is extended to many−electron systems containing first row atoms. For a given atom, two additional parameters have been incorporated into the theory to deal with the electron−electron repulsion in the valence shells. Any molecular studies using the atom are then well defined without further calibration. The molecules considered in this study are CH4, NH3, H2O, HF, C2H4, C2H2, N2H2, N2, H2O2, CO, N2O, H2CO, HCONH2, CH3F, LiCN, and LiNC. The valence basis sets in the LCAO SCF MO studies were of ’’double−zeta’’ quality. Calculated orbital energies and dipole moments for the molecules compare favorably with those from analogous all−electron calculations of Synder and Basch. Some molecular conformational calculations have also been done: the relative stability of LiNC is correctly predicted compared to LiCN; the bond angle of H2O is predicted at 105; the bond lengths of HF and N2 predicted at 1.65 and 2.44 a.u., respectively; and the barriers to internal rotation in H2O2 found to be high compared to experiment.