CHARGE INFLUENCE IN SEM-EMPIRICAL CALCULATIONS OF HETEROATOMIC IONIC AND NEUTRAL MOLECULES

Iterative extended Hükel calculations for all valence electrons and iterative PPP calculations in the variable electronegativity formalism for π-electrons were performed on benzene, pyridine, fluorobenzene, and the pyrylium ion. The charge distributions for all compounds were found more uniform and plausible with the iteration procedures than without. Polarization effects from the σ-electrons were found to be of importance for the π-electrons. The lone-pair picture of the highest occupied MO in pyridine is preserved in the iterative extended Hückel method, and two σ lone-pairs were obtained on the fluorine atom of fluorobenzene. The results indicate that this atom is not hybridized. © 1969 Springer-Verlag.