Density functional theory calculations of the electron paramagnetic resonance parameters for VO2+ complexes

Density functional theory calculations of electron paramagnetic resonance (EPR) parameters, such as electronic g tensors and metal hyperfine interaction (A) tensors, have been completed for a series of VO2+ complexes. g tensors were calculated with the zeroth-order regular approximation (ZORA) for relativistic effects as incorporated into the Amsterdam Density Functional (ADF) program. The A tensors were calculated by relativistic and nonrelativistic methods as implemented in ADF and Gaussian98 programs, respectively. The best overall agreement with experimental A values was obtained with the nonrelativistic method and the half-and-half hybrid functionals, such as BHPW91, BHP86, and B14LYP. The isotropic A values (A(iso)) calculated nonrelativistically with the BHPW91 functional deviated by about 10% from the experimental A(iso) values. The A(iso) values calculated with the relativistic effects and pure generalized gradient correction (GGA) functionals, such as BP86, deviated systematically by approximately 40% compared to the experimental A(iso) values. The difference in performance of the two methods for these complexes is attributed to the improved performance of hybrid functionals for treating core shell spin polarization. The calculation of the anisotropic or dipolar hyperfine interactions, A(D), was less sensitive to the choice of functional, and therefore, the relativistic and nonrelativistic calculations of A(D) exhibited comparable accuracy.