Hetero-atomic molecules: semi-empirical (π+σ) molecular orbital calculations and prediction of physical properties

Abstract

The LW–SCF–PPP–LCAO–MO (π+σ) method is extended to molecules containing the C–O and C–N bonds. Several modifications are made, including a new minimization of the total energy with respect to geometry. Calculations use both the Hinze–Jaffe and the Thorhallson, Fisk, and Fraga valence state ionization potentials and electron affinities, and these are compared. Heats of atomization, ΔH_a, and bond lengths, R_ij of 50 heteroatomic conjugated molecules are calculated. Ionization potentials are derived from the energy levels using Koopmans' theorem, and used to assign the ionization potentials determined by recent photoelectron spectroscopy experiments. The method gives quantitatively correct results and suggests possible assignments of the photoelectron spectra.