Calibration of ⁵⁷Fe Mössbauer constants by first principles.

Electron density and eigenvalues of the 3 × 3 matrix of the electric field gradients at the (57)Fe nuclei positions have been evaluated with the periodic ab initio CRYSTAL code for a wide range of crystalline compounds, adopting different computational approaches (Hartree-Fock, gradient corrected and hybrids functionals). The robust calibration procedure, involving experimental isomer shifts and quadrupolar splittings, yields reliable Mössbauer parameters, i.e. the isomer shift constant (α) and the nuclear quadrupolar moment (Q). Dependence of the results on the Hamiltonian is explored and well suited localized basis sets for periodic calculations are provided.