Improved CNDO/S Calculation of Electronic Spectra of Organic Compounds. I. New CNDO/S Calculation by Using an Improved Method of One-Center Electron Repulsion Integral

Abstract

The NM-γ CNDO/S program previously developed by our group was modified by the introduction of a new one-center electron repulsion integral γ_AA^new approximation, namely, the γ_AA^new-CNDO/S method. The value of this γ_AA^new was evaluated according to the product values of the coefficient C with the γ_AA value proposed in our previous paper. This method using a new γ_AA was also found to improve the two-center electron repulsion integral γ_AB value with respect to the chemical softness proposed by Nishimoto and co-workers, together with the difference between HOMO and LUMO orbital energies. The results calculated by the present improved γ_AA^new-CNDO/S method demonstrated that not only the calculated absorption maxima wavelengths and ionization potentials, but also the order and the assignment of orbitals coincided very well with those based on the results of experiments investigating a variety of polyenes, cyanynes, and polycyclic aromatic hydrocarbons.