Abstract
The prediction of isomer shifts in 57Fe Mossbauer spectra is typically achieved by building calibration lines using the values of the density at the nuclear position. Using Slater-type orbital basis or large and specific Gaussian-type orbital basis has been thus far mandatory to achieve accurate predictions with density functional theory methods. In this work, we show that replacing the value of the density at the nucleus by the density integrated in a sphere of radius 0.06 au centered on the Fe nuclei yields excellent calibration lines (r2 = 0.976) with a high predictive power (q2 = 0.975, MAE = 0.055 mm·s–1) while using the conventional def2-TZVP basis set and X-ray geometrical parameters. Our data set comprises 69 57Fe-containing compounds and 103 signals. We also find B3LYP performing significantly better than the PW91 functional.
Highlights
Since the discovery of the recoilless nuclear resonance fluorescence by Rudolf Mössbauer in 1958,1 Mössbauer spectroscopy has become a very important experimental technique, especially used for studying transition-metal compounds and metalloproteins, providing valuable information about their electronic and geometric characteristics.[2]
It can be seen that replacing ρFe(0) by ⟨ρFe⟩R leads to a systematic increase of the r2 values of the calibration lines for both functionals up until ca
The calibration lines obtained using this optimal R value are significantly better than those obtained using the values of the density at the nuclear position, especially for the PW91 functional
Summary
Since the discovery of the recoilless nuclear resonance fluorescence by Rudolf Mössbauer in 1958,1 Mössbauer spectroscopy has become a very important experimental technique, especially used for studying transition-metal compounds and metalloproteins, providing valuable information about their electronic and geometric characteristics.[2] The most used element is by far the 57Fe nucleus as it is essential, very abundant in biological systems, and the quality of the signal is good.[3−6]. From the Mössbauer spectrum, one can extract two relevant parameters, namely the isomer shift (IS) and the quadrupole splitting (QS). The QS of an 57Fe nucleus for the nuclear excited state (I = 3/2) is expressed as ΔEQ = e0QVzz 2 ikjjjjj1 + η2 3 y{zzzzz1/2 (1). Where e0 is the electron charge, Q is the quadrupole moment of the 57Fe nucleus (the value of 0.16 barn determined by Dufek et al.[7] is typically used), and the asymmetry parameter η is defined as η = Vxx − Vyy Vzz (2). QS can nowadays be directly evaluated with most codes, using electronic structure methods such as Kohn−Sham density functional theory (KS-DFT)
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