Calculation of ESR coupling constants by means of the unrestricted Hartree-Fock method

Abstract

We present a simple and straightforward procedure for the derivation of ESR coupling constants from the results of unrestricted Hartree-Fock calculations. We combine the spin orbitals into α-β pairs with similar but slightly different orbital parts; in addition there is a single unpaired orbital. After correcting the UHF results for spin contamination, the spin density is obtained as the sum of the contribution from the unpaired orbital and one-third of the contributions from all the paired orbitals. As an example we present calculations for the methyl, ethyl, vinyl, and allyl radicals based on ab initio wave functions, and we obtain satisfactory agreement with the experimental data.