Calculation of the EPR g-tensors of high-spin radicals with density functional theory

The second-order DFT approach of Schreckenbach and Ziegler to the computati on of EPR g tensors of doublet radicals (J. Phys. Chem. A 1997, 101, 3388), has been generalized to arbitrary spatially nondegenerate electronic state s. The new technique is applied to a large number (47) of diatomic main-gro up radicals, in (n)Sigma (n > 2) ground states. Calculated principal compon ents, of the EPR g tensors, are in a good agreement with experiment for mai n group radicals, with the average errors approaching the accuracy availabl e in experimental matrix isolation studies (VWN average absolute error: 3.8 ppt). The agreement with experiment deteriorates for the mixed, main group -transition metal radicals (VWN error: 8.1 ppt) but the major trends in Del tag(perpendicular to) values are still reproduced. The approach largely bre aks down for radicals containing chemical bonds between two transition meta l atoms (VWN error: 30 ppt). In all cases, the calculated g tensors are ins ensitive to the choice of the approximate exchange-correlation functional, with the simple VWN LDA, and gradient-corrected BP86 and RPBE functionals, giving essentially identical results. As an example of the possible future applications of the technique, we examine the g-tensor of the first B-3(u) excited state of the trans(CNSSS)(2)(2+) cation. Our calculations for this systems agree well with the experimental results, both for the magnitudes, and for the orientations of the principal components.