Study of lone pair description in molecules by the modified delocalized floating spherical Gaussian orbital method.

This research has been carried out to study and find a rather general description for a lone pair orbital in molecules. Since the orbital parameters must be manageable in advance, and correct geometry of the molecule (bond lengths) is depend on the appropriate lone pair description; the FSGO method including optimization has been used to obtain orbital parameters and energy. The proposed models for lone pair description have been tested by two molecules: HF and NH.29 models for HF and 23 models for NH have been used to obtain simultaneously correct bond length and dipole momentum. We show that contribution of lone pair electrons in binding gives satisfactory results. An approach which we called “Modified Delocalized Floating spherical Gaussian orbital (MDFSGO)” method was performed for these molecules. The linear combination of p-type and s-type orbital are tested. They can predict only correct bond length or dipole momentum, but the contribution of lone pair electrons in binding can predict rather satisfactory results for both bond length and dipole momentum. By using this method, the error of dipole moment and bond length decrease from 229.75% to %9.72 and from 27.28% to 4.03% in HF molecule. For NH, the error of dipole momentum changes from 256.45% to 8.023% and for bond length from 32.84% to 1.92%.