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

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.