On the calculation of Mössbauer isomer shift

Abstract

A quantum chemical computational scheme for the calculation of isomer shift in Mossbauer spectroscopy is suggested. Within the described scheme, the isomer shift is treated as a derivative of the total electronic energy with respect to the radius of a finite nucleus. The explicit use of a finite nucleus model in the calculations enables one to incorporate straightforwardly the effects of relativity and electron correlation. The results of benchmark calculations carried out for several iron complexes as well as for a number of atoms and atomic ions are presented and compared with the available experimental and theoretical data.

DFT Approach to the Calculation of Mössbauer Isomer Shifts

“…20 Then the isomer shifts were calculated from eq 5, where the proportionality constant (a ) -0.1573a 0 3 mm s -1 ) is determined from the experimental parameters of the 57 Fe nuclear transitions reported in ref 3.…”

“…[12][13][14][15][16] The so-obtained parameters of nuclear transitions may differ by a factor of 2 from the experimentally obtained values. 3 Recently, a new approach 20 to the calculation of MIS was suggested. Within this approach, the energy shift of the nuclear γ-transition is expressed in terms of the derivative of the electronic energy with respect to the radius of a finite nucleus.…”

“…20 The calculations have been carried out for a number of atoms and a series of iron clusters. The major idea underlying these benchmark calculations was to demonstrate the applicability of the new approach to the calculation of MIS and to demonstrate that the use of empirically adjusted parameters can be avoided with the use of the new method.…”

“…The major idea underlying these benchmark calculations was to demonstrate the applicability of the new approach to the calculation of MIS and to demonstrate that the use of empirically adjusted parameters can be avoided with the use of the new method. 20 However, several questions remained open in the initial study. In particular, the dependence of the results on the basis set truncation was not addressed.…”

Theoretical 57Fe Mössbauer spectroscopy: isomer shifts of [Fe]-hydrogenase intermediates

“…19,20 In this model the isomer shift is calculated directly from 5 using a value of α = −0.31 ± 0.04 a 3 0 mm s −1 from life-time measurements by Ladrière et al 21 At the same time, it was also recommended to employ effective densitiesρ which take into account the finite size of the nuclei. In order to include both relativity and sophisticated computational methods, Kurian and Filatov alternatively proposed 22 to scale non-relativistic effective densities obtained from DFT with a factorρ rel /ρ non-rel computed from CCSD(T) effective density calculations on atomic iron.…”