Calibration of the isomer shift for the14.4−keVtransition inFe57using the full-potential linearized augmented plane-wave method

First principles calculation of Mössbauer isomer shift

“…The numeric value of˛(and of R/R) shows strong dependence on the choice of the particular density functional and the basis set employed in the calculations and can vary by as much as 20-30%. Thus, the values in the range −0.253 to −0.367a 3 0 mm s −1 were obtained by different authors for the calibration constant˛of 57 Fe, which leads to the values of R/R varying in the range −0.89 × 10 −3 to −1.30 × 10 −3 [56,77,81,82]. It should be noticed however that modern density functionals do not correctly describe the electron-electron interaction potential in the vicinity of nucleus.…”

“…(7). In these calculations [52][53][54][55][56], the relativistic electron density (obtained in scalar-relativistic formalism with point-charge nucleus) was averaged over a spherical volume with the nuclear charge radius (3). In atomic calculations, a similar approach was used by Mallow et al [50] to bypass a singularity of the relativistic wave function obtained with the point-charge nucleus.…”

“…There exists a large variety of approximate density functionals which enable one to obtain results of acceptable accuracy for geometry and thermochemistry of large molecules. Although the methods related to density functional theory, such as the X␣ method [83], were employed for the interpretation of Mössbauer spectra for a long time [84][85][86][87][88][89], the use of more accurate density functional approaches in these calculations was initiated relatively recently [56,58,77,81,82,[90][91][92].…”

“…Density functional calculations of molecular models of solids [58,77,81,82,[90][91][92] as well as band structure calculations [55,56] have been employed to obtain the contact densities in iron compounds. Large sets of iron-containing species have been used in the calculations to reduce the dependence of the calibration constant on the choice of the training set of compounds.…”

“…On the basis of comparison between the relativistic and the non-relativistic isomer shifts obtained with the use of the same formalism, it was found that inclusion of relativity is important for obtaining accurate results from molecular (cluster) models. It is noteworthy that scalar-relativistic solid-state calculations are routinely carried out in the study of Mössbauer parameters of crystalline solids [53,55,56,87,[100][101][102]105,106,131].…”