What is it about?
Calculated x-ray absorption spectra (XANES, XMCD) are always broadened to account for the finite lifetime of the core hole. This broadening is often done by doing the calculations for an imaginary potential. We argue that care must be given so that this procedure does not distort the spectra at the very edge and give guidelines to make an optimal choice of the value of the imaginary potential.
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Why is it important?
The fact that broadening the spectra by means of an imaginary potential can in principle lead to distortions close to the edge has been known for some time already. However, it has been tacitly ignored up to now. We present example where proceeding along "common lines" would introduce spurious fine structure at the x-ray magnetic circular dichroism (XMCD) spectra.
Perspectives
This paper may stimulate a deeper understanding of a technical procedure that is widely used and yet its risks are not always considered. By following the guidelines given in the paper, some unpleasant surprises can be avoided.
Ondrej Sipr
Institute of Physics Czech Academy of Sciences
Read the Original
This page is a summary of: Finite lifetime broadening of calculated X-ray absorption spectra: possible artefacts close to the edge, Journal of Synchrotron Radiation, February 2018, International Union of Crystallography,
DOI: 10.1107/s1600577518000048.
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