A study of lone pair description in molecules by the floating spherical gaussian orbital (FSGO) method. Part 2

Abstract

This research is a continuation of a previously published paper with the aim of studying and finding a general description of lone pair orbitals in molecules. The orbital parameters must be known in advance, and the correct geometry of the molecule (bond angles and bond lengths) is dependent upon the appropriate lone pair description, so the floating spherical gaussian orbital (FSGO) method including optimization has been used to obtain the orbital parameters and nuclear coordinates corresponding to minimum energy. The proposed models for lone pair description have been tested by four molecules: CH 2 (singlet) and the ground states of NH 3, H 2O, and F 2. Five models have been used to obtain simultaneously correct bond lengths and bond angles. The linear combination of single p-type and 1s-type orbitals for description of a lone pair can predict only correct bond lengths 2.101 Da for CH 2; 1.909 Da for NH 3; 1.808 Da for H 2O; 2.681 Da for F 2. The linear combination of double p-type and 2s-type orbitals for describing a lone pair can predict rather satisfactory results for both bond lengths and bond angles: 2.120 Da, 102.255° for CH 2; 1.893 Da, 106.744° for NH 3; 1.723 Da, 104.315° for H 2O.