Magnetic and Spectroscopic Properties of Mixed Valence Manganese(III,IV) Dimers: A Systematic Study Using Broken Symmetry Density Functional Theory

Exchange coupling parameters and isotropic 55Mn hyperfine couplings of fourteen mixed-valence Mn(III)−Mn(IV) dimers are determined using broken-symmetry density functional theory (DFT) and spin projection techniques. A systematic evaluation of density functional approaches shows that the TPSSh functional yields the best exchange coupling constants among all investigated methods, with deviations from experiment of the order of ∼10−15%. For the prediction of 55Mn hyperfine couplings the deficiencies of DFT in the description of core-level spin-polarization and the neglect of scalar relativistic effects lead to systematic deviations between theory and experiment that can be compensated through the use of a universal scaling factor. We determine this scaling factor to be 1.49 and demonstrate that the 55Mn hyperfine couplings in mixed-valence Mn(III,IV) dimers can be successfully and systematically predicted with the TPSSh functional and the proposed spin projection techniques. The dependence of isotropic 55Mn hyperfine couplings on the Mn(III) zero-field splitting values is studied in detail using a dimer for which the strong exchange approximation breaks down. In this case we apply a rigorous form of our spin projection technique that incorporates zero-field splitting contributions to the site spin expectation values. These results form the basis for future studies that aim at deducing unknown structures on the basis of computed spectroscopic parameters.