[Wien] Error while treating Sm 4f states as core

[Laurence Marks]

Dear Anup,

Getting DFT to come close is going to be a challenge. You may find DOI:
10.1103/PhysRevMaterials.2.025001 useful. Some general comments:

1) In my experience +U is too harsh for 4f electrons. In your case 6eV is
not that far below E_F and may well be in the same energy range as states
for other elements (e.g. O). +U will force the occupied 4f low, the
unoccupied high and this may not be appropriate.

2) The width of the valence region will be too small, because you are not
including core hole effects.

3) The tabulated cross-sections for 4f  (e.g. NIST) are horribly bad --
this is know experimentally but I do not know of any better calculations.

4) There is the problem of Spin-Orbit. One also has to worry about whether
the correct parity of states is in the DFT, it is easy to get the wrong
ones at least in the rare earth scandates.

On Sun, Oct 20, 2019 at 1:49 PM Anup Shakya <npshakya31 at gmail.com> wrote:

> Dear Prof. Laurence,
>
> Thank you for your question. I have performed some magnetic measurements
> on the sample for which I am doing DFT calculations, which suggests Sm to
> be in Sm+3 state. At the same time I have performed ARPES measurements on
> the single crystalline material, and from the ARPES measurements (which I
> have performed) and the previous ARPES report on this sample it seems that
> there are no Sm 4f states near the Fermi energy. This also suggests that Sm
> exist in Sm+3 state. Now since Sm+3 state has an energy far below the Fermi
> level around -6 eV and only Sm +2 states lie near the Fermi level (JPS
> Conf. Proc. 3, 017038 (2014). So, I wanted to reproduce the band structure
> by treating Sm 4f as core states and compare the DFT results  and the ARPES
> results. The other reason is that when I am doing GGA+U calculations using
> various values of U, the DFT results are not matching with the observed
> ARPES spectra. Looking forward to hearing from you.
>
> SIncerely,
> Anup Pradhan Sakhya
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-- 
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu
Corrosion in 4D: www.numis.northwestern.edu/MURI
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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