Prediction of Iron K-Edge Absorption Spectra Using Time-Dependent Density Functional Theory

Abstract

Iron K-edge X-ray absorption pre-edge features have been calculated using a time-dependent density functional approach. The influence of functional, solvation, and relativistic effects on the calculated energies and intensities has been examined by correlation of the calculated parameters to experimental data on a series of 10 iron model complexes, which span a range of high-spin and low-spin ferrous and ferric complexes in O(h) to T(d) geometries. Both quadrupole and dipole contributions to the spectra have been calculated. We find that good agreement between theory and experiment is obtained by using the BP86 functional with the CP(PPP) basis set on the Fe and TZVP one of the remaining atoms. Inclusion of solvation yields a small improvement in the calculated energies. However, the inclusion of scalar relativistic effects did not yield any improved correlation with experiment. The use of these methods to uniquely assign individual spectral transitions and to examine experimental contributions to backbonding is discussed.

Structure of the FeBTC Metal–Organic Framework: A Model Based on the Local Environment Study

“…The well-defined absorption feature clearly visible in all spectra is characteristic of the Fe K-edge and is known to arise from the 1s -> 3d transition. 19 The superimposition of the pre-edge of the sample and reference signals bring to an analogous result coming from the comparison between the edge positions ( fig.1). Noticeably, both the shape and the position of the pre-edge of the experimental data are in agreement to the signal of Fe 3+ and don't fit the Fe 2+ signal.…”

Probing the electronic and geometric structure of ferric and ferrous myoglobins in physiological solutions by Fe K-edge absorption spectroscopy

“…In addition, the present analysis enables us to quantify the magnitude of the heme doming in the unligated form (deoxyMb). Finally, the electronic structure is investigated using the pre-edge structures, analysed with time-dependent density functional theory (TD-DFT), 61,62 implemented within the ORCA quantum chemistry package. 63,64 We find that these features are predominantly 1s -d s and 1s -d p À p ligand * transitions, while 1s -d p transitions also weakly contribute for MbO 2 , metMb and deoxyMb.…”

Revisiting the Dependence of Cu K-Edge X-Ray Absorption Spectra on Oxidation State and Coordination Environment

“…Details on the Computational Methodology are given in the corresponding section below. We note that an empirical, methoddependent constant shift has to be applied in order to align the calculated spectra with experiment [32,33]. Here, a consistent shift has been applied to all spectra calculated with the same method, even though different types of complexes (e.g., with different charge states) might require a different shift [33,34].…”