Validation study of meta-GGA functionals and of a model exchange-correlation potential in density functional calculations of EPR parameters

We report the first implementation of the DFT calculation of electronic g-tensors and hyperfine coupling constants using meta-GGA exchange-correlation functionals (both Laplacian and kinetic-energy-density dependent) and statistical average of orbital model exchange-correlation potentials (SAOP). The g-tensors for a set of eleven small main group radicals and for a series of ten 3d and two 4d transition metal complexes have been compared using two meta-GGA functionals (FT98 and PKZB), SAOP, as well as the BP86 GGA, and B3PW91 and BHPW91 hybrid functionals. The same functionals have been compared in the calculation of hyperfine coupling constants for thirteen small main group radicals and twelve 3d transition metal compounds. The results for main group radicals are satisfactory, both with the newly validated and previously tested functionals. In contrast, the accurate evaluation of the EPR parameters for 3d transition metal complexes remains a challenge for pure density functional theory: the new functionals (potentials) do not improve the results compared to GGA functionals, whereas hybrid functionals tend to provide superior results. SAOP leads to large spin contamination for a number of transition metal complexes. This has been traced back to the orbital-energy dependence of the potential.