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

Abstract

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 (C 6H 6 +), the benzene anion (C 6H 6 −), hydropyrazine (C 4H 5N 2), the dihydropyrazine cation (C 4H 6N 2 +), the aniline radical (C 6H 5NH), the p-benzoquinone anion (C 6H 4O 2 −), phenoxyl (C 6H 5O), the nitrobenzene anion (C 6H 5NO 2 −), and the nitropyridine anion (C 5H 4N 2O 2 −). 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.