Calibration of 57Fe isomer shift from ab initio calculations: can theory and experiment reach an agreement?

Abstract

Using linear response approach to the Mössbauer isomer shift, the calibration constant α(⁵⁷Fe) was obtained from high level ab initio calculations carried out for a representative set of iron compounds. The importance of the effects of relativity and electron correlation for an accurate description of the ⁵⁷Fe isomer shift is demonstrated on the basis of the Hartree–Fock, coupled cluster with singles and doubles and of the double hybrid density functional calculations. A reliable value of the calibration constant (α(⁵⁷Fe) = −0.306 ± 0.009 mm s⁻¹) was obtained with the use of the B2-PLYP double hybrid density functional. This value is in good agreement with the experimentally estimated constant of −0.31 ± 0.04 a³₀ mm s⁻¹ and can be recommended for theoretical modeling of ⁵⁷Fe isomer shifts.