Correlation Effects of π Electrons. II. Low-Lying Excitations of Polycyclic Hydrocarbons

We show how the Coulomb interaction between $\pi$ electrons in a conjugated molecule is screened by the presence of the other $\pi$ electrons. We describe how the resulting effective interaction can be calculated and used in a configuration‐interaction calculation to determine the low‐lying excitations of such molecules. The methods are applied to the study of a series of hydrocarbons from benzene to hexabenzocoronene and good agreement with the experimental spectra is obtained. The inclusion of these correlation effects predicts a characteristic nonuniform distribution of charge in alternant hydrocarbons.