Hartree-Fock linear response calculations of g-tensors of substituted benzene radicals

Linear response theory has been applied for calculations of g-tensors of organic radicals in order to test the range of validity of restricted Hartree-Fock reference states. The g-values were calculated for the benzene cation (C6H6+), the benzene anion (C6H6-), hydropyrazine (C4H5N2), the dihydropyrazine cation (C4H6N2+), the aniline radical (C6H5NH), the p-benzoquinone anion (C6H4O2-), phenoxyl (C6H5O), the nitrobenzene anion (C6H5NO2-), and the nitropyridine anion (C5H4N2O2-). Influence of variations of structural parameters on the g-tensor components were investigated. Calculated g-values were in excellent agreement with experiment for six out of nine radicals. Two radicals - the p-benzoquinone anion and aniline radical - showed minor discrepancies, while the g-tensor of the phenoxyl radical was incorrect. The problem with the phenoxyl radical was traced to a complex electronic structure and optical spectrum. Results consistent with experiment could in that case only be obtained with electron correlated calculations. (C) 1999 Elsevier Science B.V. All rights reserved.