First principles theoretical modeling of the isomer shift of Mössbauer spectra

PhD ceremony: Ms. R. Kurian, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Title: First principles theoretical modeling of the isomer shift of Mössbauer spectra

Promotor(s): prof. M. Filatov

Faculty: Mathematics and Natural Sciences

 

The Mössbauer spectroscopy parameters such as the isomer shift, quadrupole splitting and magnetic hyperfine splitting carry substantial information on the electronic structure, spin- and oxidation states of the resonating atom. This dissertation is focused mainly on the isomer shifts, which is a measure of energy difference between the energies of gamma-transitions occurring in the sample (absorber) nucleus compared to the reference (source) nucleus. Because the electronic environments in which the sample and the reference nuclei immersed are different, the isomer shift probes this difference. However the interpretation of the relationship between the isomer shift and the electronic structure is not straight forward and the first principle models are essential. The existing traditional perturbational treatments of the isomer shifts are not very accurate and lack some essential characteristics. This dissertation details a new approach developed recently [J. Chem. Phys. 127, 084101 (2007)], within which the isomer shift is expressed as the derivative of electronic energy with respect to the nuclear radius, it has the clear advantage that relativistic and electron correlation effects can be directly included in the calculation. With the use of the linear response formalism, the performance of various density functionals were analysed and reliable parametrization of ⁵⁷Fe and ¹¹⁹Sn nuclei were obtained, which are detailed in this dissertation. The application of the calculated calibration parameters for the investigation on various iron based systems such as the Prussian blue analogues and recently discovered high temperature superconductors are described in this dissertation.