Estimation of two-center electron repulsion integrals based on the absolute hardness calculated by the PPP molecular orbital method

Abstract

In order to improve the precision of the prediction of the electronic spectra of organic dyes, novel two-center electron repulsion integral, new-gamma, for the PPP molecular orbital method has been investigated. In this paper we propose the estimation of the spectrochemical softness parameter (k-value) in new-gamma using the absolute hardness from PPP (N*M-gamma) or Hueckel method, and report the calculated wavelengths of the first absorption maxima of the anthraquinones, diarylmethans, and cyanine derivatives. The wavelengths calculated by the PPP method with the k values obtained from the absolute hardness represented the observed values better than the other methods.