[Wien] Photon energies in XES ...

[Laurence Marks]

There is a lot of literature on this. Have you looked at (for instance) the
work of Les Allen, as well as the work of the group who wrote the TELNES
script?

N.B., "electron gun", not "electronic gun". Electronic microscope is an all
too common typo.

On Fri, Aug 28, 2015 at 10:19 AM, Vladimir Timoshevskii <
vladimir at physics.mcgill.ca> wrote:

> Dear Wien2k users and developers,
>
> I am working with experimentalists and try to simulate the XES measured by
> soft x-ray detector, coupled with electron microscope. So, the ionization
> source in this setup is the electronic gun of the TEM. The test compound is
> hexagonal layered BN, which was quite well studied before, including the
> similar setup. I would greatly appreciate if you could share your opinion
> on the following 2 issues, which I am facing now:
>
> i) Is it possible, in principle, to obtain correct photon energies instead
> of shifting spectrum by hand to the EF position? I understand, that the
> position of the core level (B-1s) is sensitive to the form of the potential
> well, and the closer my potential is to the real one, the better is the
> position of the core level. I tried different XC-functionals, and found
> that actually the atomic-like Hartree-Fock gives the best results: the
> whole spectrum (B K-edge) is shifted to higher energies, closer to
> experiment, and the spectrum shape is also much better. However, there is
> still ~10eV shift, relative to the experimental spectrum. So, the
> XC-functional alone does not solve this problem ...
>
> ii) This is a more fundamental question, and is actually related to the
> first one. I guess, the main reason for the photon energy underestimation
> is the presence of the core hole, which shifts the ionized core level to
> lower energies. I did several test calculations of B-K spectrum using
> supercells of diffferent sizes with a core hole in B 1s. Indeed, by playing
> with fractional B 1s occupation (trying to catch the "transition state"),
> it seems to be possible to shift the whole spectrum to experimental
> position. But in this case, what about the "rule of the final state"?
> According to this rule, the hole must be created in the valence band (and
> screened out), and the core lavel must be filled. This is what we normally
> assume ... Does that mean that the XES calculations with hole in the core
> are unphysical, in spite of giving better photon energies? May be, the
> situation here, especially when we use TEM electronic gun for core
> ionization,  is more complicated? In my opinion, the valence-core
> transitions are happening in the potential, already distorted by the
> presence of the core hole. Am I right? Then, how it agrees with the "rule
> of the final state"? Any thoughts on that would be highly appreciated!
>
> Thanks a lot in advance!
>
> Vladimir Timoshevskii
>
>
>



-- 
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu
Corrosion in 4D: MURI4D.numis.northwestern.edu
Co-Editor, Acta Cryst A
"Research is to see what everybody else has seen, and to think what nobody
else has thought"
Albert Szent-Gyorgi
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