[Wien] Occupying high energy states without FERMI error

[Peter Blaha]

Hi,

It is not quite clear to me what you acutally want to do.

When you do photoemission, why do you want to occupy conduction band 
states ?

Core hole calculations are for core-photoemission the proper choice.
For valence photoemission we usually neglect the hole in the valence 
bands - although this can be a crude approximation for more localized 
states.

In optical spectroscopy one would do what you describe: transfer a 
valence electron into the conduction band.
The best approach would be to use the Bethe-Salpeter approach (the BSE 
code is available on request for WIEN2k - see unsupported software). 
This treats excitonic effects quite accurately, but is also quite 
demanding (needs a large computer cluster).

If I understand your approach correctly, you reduced the number of 
valence electrons and put the missing charge as background ??
In this way you excite only electrons at the VBM !!!
How many electrons would you remove ? If you remove 1 electron, you 
remove it in every unit cell of your infinite crystal !! This is not 
what happens in experiment.
You could create a supercell (eg. 2x2x2) and excite 1 e, but again, 
usually this is "delocalized" and you will remove 1/8 of an electron in 
each cell of the whole crystal.

PS: "Technically" it should still be possible to use a "2-window" 
calculation (previously used for semicore states) in WIEN2k. You can run 
lapw2 two (3) times, once with NE-1 electrons and once with NE+1 
electrons and set an appropriate EMIN in lapw2  (x lapw2 -sc -emin xxx), 
where xxx could be EF of the ground state).  Mixer will then add the 
clmval and clmsc files together. But you always have the problem: you do 
this for the whole crystal).

Am 15.09.2020 um 22:26 schrieb Guoping Zhang:
> Dear Professor Blaha and Wien users,
> 
> I am interested in states in conduction bands, but I am not interested 
> to get a Fermi energy (and I have no Fermi error in the ground state run).
> I occupy some conduction states (removing some from valence bands) with 
> some electrons by changing the weight files. If I use the Tetrahedral 
> method, this leads to Fermi error in fermi.F at SOS. (TEMPS option in 
> case.in2 is not ideal for my case).   So I calculate the electron 
> difference between NOS(1)  and RNTOT in the NOS subroutine, and put this 
> difference  into case.inm as a background charge. Wien2k runs  without 
> an Fermi error message, but I wonder
> (1) whether this is a sound approach.
> (2) whether there is any other better method, besides creating a core 
> hole in case.inc file.
> (3) whether this method can be used to treat photoemission, where 
> electrons are knocked out of the system.
> 
> Any comments and suggestions are welcome. If you need more information, 
> I will be happy to provide.
> 
> Thank you very much for your help and attention!
> Best wishes,
> Guoping
> 
> 
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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