The effect of changing the method of calculating repulsion integrals within the framework of the semiempirical self-consistent field method is investigated with respect to the transition energies of the alternant hydrocarbons benzene, anthracene, phenanthrene, and pyrene. Of the methods investigated, the one originally suggested by Mataga gave the best agreement with experiment. By statistical analysis of the linear relationship between the internuclear distance rpq and the bond order p,,, the regression lineThe success of the Hiickel LCAO procedure in correlating observed p-band transition energies with the Hiickel energy number ( N P = No. of atoms contributing T electrons) for the highest occupied MO was shown to be due to ( 1 ) the relative unimportance of configuration interaction for this transition, (2) the invariance of the electron interaction terms calculated by the S C F method for different hydrocarbons, and (3) the identity of the Hiickel energy number K$ with the corresponding term
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