COMPARISON OF DENSITY-FUNCTIONAL AND HARTREE-FOCK AVERAGE LOCAL IONIZATION ENERGIES ON MOLECULAR-SURFACES

We investigated whether an average local ionization energy defined wit hin the framework of Hartree-Fock theory is physically meaningful in K ohn-Sham density functional theory, in view of the uncertainty in rela ting the latter orbital energies to electronic ionization energies, in a preliminary study of N2O using several different exchange/correlati on functional combinations, it was found that the orbital energies in each case correlate roughly with experimental binding energies. Averag e local ionization energies are computed on the molecular surfaces of 11 monosubstituted benzene derivatives using both Hartree-Fock and den sity functional procedures. Both sets of results correctly predict the ortho/para- or meta-directing tendencies of the substituents, as well as their ring-activating or -deactivating effects. Excellent correlat ions were obtained with the Hammett substituent constants. This initia l study suggests that Kohn-Sham average local ionization energies shou ld be physically meaningful, on a relative basis. (C) 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 607-613, 1998.