[Wien] ReSi2 - semi-core states are missing from DOS

[Peter Blaha]

a) Missing DOS of core states:
You calculate the DOS on an E-grid with a spacing of 3 mRy. Your core 
states have such a small band dispersion (eg. just one 1mRy, but 
sometimes even below; check the band ranges), and their energies fall 
BETWEEN your DOS E-grid, so on your grid there is really no DOS. In 
case.outputt you should see that at the expected energies, the 
"integreated DOS" increases from one energy mesh to the next by 2, 6 or 
even 14 electrons, although the DOS at these energies is always zero.

In essence: It is meaningless to "plot a DOS" of these localized states, 
as it would corresponds to almost a delta-peak at a particular energy.
Also note, that in DFT the energy of a core level has really no 
particular meaning anyway and will be far from any measurement (10 % 
error in E-position)

b) XPS of 4f core states:
I would strongly recommend to put these states into the core. This can 
be done conveniently during init_lapw in lstart, by not using an Energy 
criterium (like -6 or -8 Ry), but a "localization criterium" like 0.999 
. If you check the localization of the 4f states during lstart, you will 
see that nearly everything is within the atomic sphere.
The advantage of this core treatment is 2-fold: spin-orbit coupling is 
included nearly exactly (and not approximative in lapwso); and a 
"half-core hole" calculation based on Slaters transition state theory 
should even give you fairly accurate absolute energies.
Remember: the core states are recalculated in the modified crystal 
potential, so the effect of charge transfer, ... is covered. A direct 
hybridization with other states is anyway zero (as you can see from your 
band width when you put them as semicore state) and there is no need to 
allow for it in principle (but spoiling the much more important 
spin-orbit coupling). It is in general NOT true that inclusion of more 
core states increases the "accuracy" ....

Am 01.02.2017 um 13:07 schrieb Yevgen Melikhov:
> Dear WIEN2k users,
>
> I recently started studying ReSi2 and was immediately puzzled while
> doing basic SCF and DOS calculations.
>
> The structure file is attached, RMT of Re is 2.2, RMT of Si is 2.03.
>
> Initialization was done with the following parameters:
> init_lapw -b -vxc 5 -ecut -8 -rkmax 8 -numk 1000 -sp
>
> Checking the output (also attached) I can see that:
> For Re
> States 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d are treated as core states
> States 5s, 5p, 4f may be considered as semi-core states (energy range:
> -6.29…-3 Ry)
> States 5d, 6s are considered as valence states
> For Si:
> States 1s, 2s are treated as core states
> States 2p may be considered as semi-core states (energy around: -7 Ry)
> States 3s, 3p are considered as valence states
>
> After Running SCF calculations with:
> runsp_lapw -p -ec 0.00001 -cc 0.0001 -NI
> and calculating DOS, I found out that I do not see 4f of Re (which I
> expect to be at -40 eV as a huge peak), 5s of Re (-80 eV), or 2p of Si
> (-90 eV) at all (!!!) Please see attached the figures of DOS. (I also
> attach int-file to make sure that I did want DOS starting from -10.5 Ry)
>
> I am really puzzled with this and will be grateful for any
> comments/suggestions.
>
> P.S. My ultimate goal is to calculate XPS spectra to be able to see
> 4f7/2 and 4f5/2 splitting. I guess for this I will have to introduce a
> hole (?) in a semi-core state. I know how to do that in a core-state but
> I am not sure how to do that for a semi-core. Any comments/suggestions
> on this matter will be received with much appreciation as well.
>
> Thank you in advance for your help,
> Yevgen Melikhov.
> (Institute of Physics PAS, Warsaw)
>
>
>
>
>
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
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