Development and validation of reliable quantum mechanical approaches for the study of free radicals in solution

The hyperfine parameters of a number of representative free radicals have been computed by post-Hartree-Fock and density functional approaches including averaging effects from large amplitude vibrations and solvent effects through a recent implementation of the polarizable continuum model. Our results show that fully ab initio hyperfine splittings are accurate enough to back the interpretation of experimental data and to allow an unbiased judgement of the role played by electronic, vibrational, and environmental effects in determining the observed value. The very good results obtained by a density functional approach including some Hartree-Fock exchange both for intrinsic values and for solvent shifts pave the route for the investigation of large biologically significant radicals in their natural aqueous medium. (C) 1996 American Institute of Physics.