Calibration constant for Fe 57 Mössbauer isomer shifts derived from ab initio self-consistent-field calculations on octahedral Fe<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="…
1978; American Physical Society; Volume: 17; Issue: 1 Linguagem: Inglês
10.1103/physrevb.17.91
ISSN1095-3795
AutoresW. C. Nieuwpoort, Doeke Post, P.Th. van Duijnen,
Tópico(s)Inorganic Fluorides and Related Compounds
ResumoAb initio self-consistent-field molecular-orbital calculations were performed on octahedral Fe${\mathrm{F}}_{6}$ and Fe${(\mathrm{CN})}_{6}$ clusters using extensive basis sets of Gaussian-type functions. Two distances relevant for ferrous and ferric compounds are considered. In this paper, we report the part of our results that is relevant for a determination of the isomer-shift calibration constant for Fe. Good overall consistency with available $^{57}\mathrm{Fe}$ M\"ossbauer data is found resulting in a value of ${\ensuremath{\alpha}}_{\mathrm{HF}}=(\ensuremath{-}0.30\ifmmode\pm\else\textpm\fi{}0.03){a}_{0}^{3}$mm ${\mathrm{sec}}^{\ensuremath{-}1}$ for the calibration constant to be used in conjunction with densities on the nucleus calculated in the spin- and symmetry-restricted Hartree-Fock approximation. This value is compared with previous estimates, a number of which can be corrected on the basis of the present work and are then shown to agree with our results. Recent attempts to obtain quantitative relativistic corrections by solving the Fock-Dirac equations for Fe and its ions are discussed. A value for the calibration constant appropriate to densities calculated by this method of ${\ensuremath{\alpha}}_{\mathrm{FD}}=(\ensuremath{-}0.22\ifmmode\pm\else\textpm\fi{}0.02){a}_{0}^{3}$mm ${\mathrm{sec}}^{\ensuremath{-}1}$ is tentatively derived.
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