First principles calculation of Mössbauer isomer shift

Filatov, Michael

doi:10.1016/j.ccr.2008.05.002

Cited by 67 publications

(86 citation statements)

References 145 publications

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“…This issue has been widely discussed for isomer shifts and it seems to be a common conclusion that functionals with a high amount of exact exchange are to be preferred. 10,20 Yet, using the X2C Hamiltonian and for the molecules investigated here, we find the the PBE functional performs well and is not inferior to the hybrid version PBE0 -the latter having a high amount of exact exchange (25%). Although our present CCSD results indicate that PBE0 is more accurate, a test with a larger and more varied test set should be performed before reaching a final conclusion regarding the best suited DFT functional for the X2C Hamiltonian.…”

Section: Comparison To Experimentsmentioning

confidence: 74%

Theoretical ⁵⁷Fe Mössbauer spectroscopy: isomer shifts of [Fe]-hydrogenase intermediates

Hedegård

Knecht

Ryde

et al. 2014

Phys. Chem. Chem. Phys.

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Mössbauer spectroscopy is an indispensable technique and analytical tool in iron coordination chemistry. The linear correlation between the electron density at the nucleus ("contact density") and experimental isomer shifts has been used to link calculated contact densities to experimental isomer shifts. Here we have investigated for the first time relativistic methods of systematically increasing sophistication, including the eXact 2-Component (X2C) Hamiltonian and a finite-nucleus model, for the calculation of isomer shifts for iron compounds.While being of similar accuracy as the full four-component treatment, X2C calculations are far more efficient. We find that effects from spin orbit coupling can safely be neglected, leading to further speed up. Linear correlation plots using effective densities rather than contact densities versus experimental isomer shift leads to a correlation constant a = −0.32 a −3 0 mm s −1 (PBE functional) which is in close agreement to experimental findings. Isomer shifts of similar quality can thus be obtained both with and without fitting, which is not the case if one pursues a priori a non-relativistic model approach. As an application for a biologically relevant system, we have studied three recently proposed [Fe]-hydrogenase intermediates. The structures for these intermediates were extracted from QM/MM calculations using large QM regions surrounded by the full enzyme and a solvation shell of water molecules. We show that a comparison between calculated and experimentally observed isomer shifts can be used to discriminate between the different intermediates, whereas calculated atomic charges do not necessarily correlate with Mössbauer isomer shifts. Detailed analysis shows that the difference in isomer shifts between two intermediates is due to an overlap effect.

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Section: Comparison To Experimentsmentioning

confidence: 74%

Theoretical ⁵⁷Fe Mössbauer spectroscopy: isomer shifts of [Fe]-hydrogenase intermediates

Hedegård

Knecht

Ryde

et al. 2014

Phys. Chem. Chem. Phys.

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“…and is a function of the nuclear radius R. Following Filatov [19,22], we calculate the associated shift in frequency of the emitted or absorbed photon as an energy derivative …”

Section: Validity Of the Contact Density Approximationmentioning

confidence: 99%

“…This is hardly a viable approach in a relativistic framework due to the weak singularity of the electron density at the nucleus. We therefore follow the approach of Filatov [19,22] in which the isomer shift is calculated as an energy derivative. We start with the clamped-nucleus approximation in which a nucleus provides an electrostatic potential that depends on the nuclear charge density q n as / n ðr e ; RÞ ¼ Z d 3 r n q n ðr n ; RÞ r ne ;…”

Section: Validity Of the Contact Density Approximationmentioning

confidence: 99%

“…By employing an extendednucleus model, one may also go beyond the contact density approximation and explicitly calculate the change in nucleus-electron interaction corresponding to the nuclear transition measured in Mössbauer spectroscopy. This approach has been pursued by Filatov and co-workers [19][20][21][22][23] who introduce a difference in radius between the ground-and excited state nucleus as a finite perturbation that can be used to numerically differentiate the electronic energy. An added advantage is that such a finite difference scheme also works for methods for which it is difficult to obtain the relaxed density directly.…”

Section: Introductionmentioning

confidence: 99%

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Mössbauer spectroscopy for heavy elements: a relativistic benchmark study of mercury

Knecht

Fux

Meer³

et al. 2011

Theor Chem Acc

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The electrostatic contribution to the Mössbauer isomer shift of mercury for the series HgF n (n = 1, 2, 4) with respect to the neutral atom has been investigated in the framework of four-and two-component relativistic theory. Replacing the integration of the electron density over the nuclear volume by the contact density (that is, the electron density at the nucleus) leads to a 10% overestimation of the isomer shift. The systematic nature of this error suggests that it can be incorporated into a correction factor, thus justifying the use of the contact density for the calculation of the Mössbauer isomer shift. The performance of a large selection of density functionals for the calculation of contact densities has been assessed by comparing with finite-field four-component relativistic coupled-cluster with single and double and perturbative triple excitations [CCSD(T)] calculations. For the absolute contact density of the mercury atom, the Density Functional Theory (DFT) calculations are in error by about 0.5%, a result that must be judged against the observation that the change in contact density along the series HgF n (n = 1, 2, 4), relevant for the isomer shift, is on the order of 50 ppm with respect to absolute densities. Contrary to previous studies of the 57 Fe isomer shift (F Neese, Inorg Chim Acta 332:181, 2002), for mercury, DFT is not able to reproduce the trends in the isomer shift provided by reference data, in our case CCSD(T) calculations, notably the non-monotonous decrease in the contact density along the series HgF n (n = 1, 2, 4). Projection analysis shows the expected reduction of the 6s 1/2 population at the mercury center with an increasing number of ligands, but also brings into light an opposing effect, namely the increasing polarization of the 6s 1/2 orbital due to increasing effective charge of the mercury atom, which explains the nonmonotonous behavior of the contact density along the series. The same analysis shows increasing covalent contributions to bonding along the series with the effective charge of the mercury atom reaching a maximum of around ?2 for HgF 4 at the DFT level, far from the formal charge ?4 suggested by the oxidation state of this recently observed species. Whereas the geometries for the linear HgF 2 and square-planar HgF 4 molecules were taken from previous computational studies, we optimized the equilibrium distance of HgF at the four-component Fock-space CCSD/aug-cc-pVQZ level, giving spectroscopic constants r e = 2.007 Å and x e = 513.5 cm -1 .Dedicated to Professor Pekka Pyykkö on the occasion of his 70th birthday and published as part of the Pyykkö Festschrift Issue.Electronic supplementary material The online version of this article

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“…However, it should be noted that this calculation includes some limitations as pointed out by Filatov and coworkers. [31] This is because Equation (2) derived by non-relativistic treatment is employed and the finite nucleus effect is not considered for ρ0 values obtained by the present ZORA-DFT calculation.…”

Section: Correlation Between ρ0 Calc and δNp Expmentioning

confidence: 99%

Computational Study on Mössbauer Isomer Shifts of Some Organic-neptunium (IV) Complexes

Kaneko¹,

Miyashita²,

Nakashima³

2015

Croat. Chem. Acta

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Relativistic DFT calculations are applied to some organo-neptunium (IV) complexes, Cp3Np IV X (Cp = η 5 -C5H5; X = BH4, Cl, OtBu, Ph, nBu), in order to understand their bonding properties between Np and the ligands. We employ scalar-relativistic ZORA Hamiltonian with all-electron basis set (SARC). The calculated electron densities at Np nucleus position in the complexes at B2PLYP / SARC theory strongly correlate to the experimental Mössbauer isomer shifts of 237 Np system. The result of bond overlap population analysis indicates that the bonding strength decreases in order of X = BH4, Cl, OtBu, Ph and nBu. The tendency depends on the degree of the covalent interaction between Np 5f-electron and X ligand. It is suggested that it is important to estimate the bonding contribution of 5f-orbital to understand the electronic state for organoactinide complexes.

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First principles calculation of Mössbauer isomer shift

Cited by 67 publications

References 145 publications

Theoretical ⁵⁷Fe Mössbauer spectroscopy: isomer shifts of [Fe]-hydrogenase intermediates

Theoretical ⁵⁷Fe Mössbauer spectroscopy: isomer shifts of [Fe]-hydrogenase intermediates

Mössbauer spectroscopy for heavy elements: a relativistic benchmark study of mercury

Computational Study on Mössbauer Isomer Shifts of Some Organic-neptunium (IV) Complexes

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First principles calculation of Mössbauer isomer shift

Cited by 67 publications

References 145 publications

Theoretical 57Fe Mössbauer spectroscopy: isomer shifts of [Fe]-hydrogenase intermediates

Theoretical 57Fe Mössbauer spectroscopy: isomer shifts of [Fe]-hydrogenase intermediates

Mössbauer spectroscopy for heavy elements: a relativistic benchmark study of mercury

Computational Study on Mössbauer Isomer Shifts of Some Organic-neptunium (IV) Complexes

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Theoretical ⁵⁷Fe Mössbauer spectroscopy: isomer shifts of [Fe]-hydrogenase intermediates

Theoretical ⁵⁷Fe Mössbauer spectroscopy: isomer shifts of [Fe]-hydrogenase intermediates