Relativistic two-component calculations of electronic g-tensor for oxo-molybdenum(V) and oxo-tungsten(V) complexes: The important role of higher-order spin-orbit contributions

In an effort towards the reliable calculation of EPR parameters of molybdenum and tungsten enzyme active sites, the effect of higher-order spin-orbit effects and of exchange-correlation functional on the electronic g-tensors of small [MVOCl5]2− and medium-sized [MVO(bdt)2]− (bdt = benzene-1,2-dithiolate), [MVOCl3(bpy)] (bpy = bipyridine) complexes (M = Mo or W) has been evaluated. Comparison of one-component calculations with perturbational treatment of spin-orbit coupling and two-component non-collinear spin density functional calculations indicate the substantial importance of higher-order spin-orbit effects, in particular for the tungsten species. Pseudopotential calculations tend to underestimate the spin-orbit effects compared to all-electron calculations based on the Douglas-Kroll-Hess Hamiltonian. Hybrid functionals with somewhat enhanced exact-exchange admixture tend to provide better agreement with experiment than pure gradient-corrected functionals.