8 research outputs found
Four-Component Relativistic Density Functional Theory Calculations of EPR g- and Hyperfine-Coupling Tensors Using Hybrid Functionals: Validation on Transition-Metal Complexes with Large Tensor Anisotropies and Higher-Order Spin-Orbit Effects
The four-component matrix Dirac-Kohn-Sham (mDKS) implementation of EPR
g- and hyperfine A-tensor calculations within a restricted kinetic balance framework in the
ReSpect code has been extended to hybrid functionals. The methodology is validated for an
extended set of small 4d1
and 5d1
[MEXn]
q
systems, and for a series of larger Ir(II) and Pt(III)
d7
complexes (S=1/2) with particularly large g-tensor anisotropies. Different density
functionals (PBE, BP86, B3LYP-xHF, PBE0-xHF) with variable exact-exchange admixture x
(ranging from 0% to 50%) have been evaluated, and the influence of structure and basis set
has been examined. Notably, hybrid functionals with exact-exchange admixture of about 40%
provide the best agreement with experiment and clearly outperform the generalized-gradient
approximation (GGA) functionals, in particular for the hyperfine couplings. Comparison with
computations at the one-component second-order perturbational level within the DouglasKroll-Hess
framework (1c-DKH), and a scaling of the speed of light at the four-component
mDKS level, provide insight into the importance of higher-order relativistic effects for both
properties. In the more extreme cases of some iridium(II) and platinum(III) complexes, the
widely used leading-order perturbational treatment of SO effects in EPR calculations fails to
reproduce not only the magnitude but also the sign of certain g-shift components (with the
contribution of higher-order SO effects amounting to several hundreds of ppt in 5d
complexes). The four-component hybrid mDKS calculations perform very well, giving
overall good agreement with the experimental data