Semiempirical calculation of electronic spectra of organic compounds by using the improved method of new-γelectron repulsion integral

摘要

electronic spectra of organic compounds were calculated by incorporating the improved method of New-γ for the two-center electron repulsion integral into two semiempirical molecular orbital methods (CNDO/S and INDO/S). In this method we improved the previously reported New-γ approximation by determining a parameter k for each bond. This method significantly improved the calculated wavelengths of linear polyenes obtained by using New-γ. We further improved this by determining an expression for a variable k in which k is a function of the bond length of C-C. This variable method well reproduced experimental electronic spectra of linear polyenes, toluene, xylene, styrene, and polyacenes. These results show that this variable method can be applied to the C-C bond in other organic compounds, such as polycyclic aromatic hydrocarbons (PAHs)