A New Benchmark to the Accurate Calculation of 57Fe Mössbauer Parameters with Density Funcitonal Theory
Image posted with permission from J. Chem. Theory Comput., 2013, 9 (11), pp 5004–5020. Copyright 2013 American Chemical Society

In a recently published paper in the Journal of Chemical Theory and Computation of the American Chemical Society (ACS), density functional theory (DFT) calculations were found to correctly reproduce the 57Fe isomer shifts (δ) and quadrupole splittings (ΔEQ) of a large and chemically very diverse set of 66 Fe complexes. For the isomer shifts, several density functionals provide accurate δ values for all investigated iron compounds, with the best-performing DFT method yielding a mean absolute error (MAE) of 0.05 mms-1 and a maximum deviation of 0.12 mms-1. Although a similarly well-performing functional could not be chosen for the prediction of quadrupole splittings, the selection of an appropriate DFT method by a careful chemical classification of Fe complexes enables the accurate prediction of this parameter: the application of this approach yields a MAE of 0.12 mms-1 (7% error) and a maximum deviation of 0.55 mms-1 (17% error) (see the figure presented above). This accuracy should be sufficient for most chemical problems that concern Fe complexes. Besides these benchmark results, special issues are also covered in the article including the prediction of ΔEQ in especially challenging cases, quadrupole splittings at phase transitions induced by variations of the electronic structure (e.g. spin crossover and inversion of the orbital ground state), as well as the reliable determination of the sign of the quadrupole splitting. The excellent agreement observed between the experimental and calculated signs of ΔEQ may immensely enhance the potential of the application of Mössbauer spectroscopy in structural research. The details of the summarized work is available at the link below.

Link to the article: http://pubs.acs.org/doi/abs/10.1021/ct4007585