[Wien] Absolute excitation energy in the x-ray absorption spectra calculation

[Peter Blaha]

In Xanes you want to put the electron into the "state" to which it is 
excited in experiment. For O-K this would be O-2p states. If your 
electronic structure is such, that the first conduction band states are 
mainly O-2p states, you should put the electron into these states. You 
can do that by simply increasing the number of electrons by on (or 
one-half) in case.in2c  (512 --> 513)
Then do scf-cycle, but before running the spectra, reduce NE back to 512.

Alternatively, if you these states are very different (or if you want to 
simulate XPS-energies (half-core hole) you put them into the "background 
"(because you need a neutral cell). (You would like to remove it 
(ionization) or put it into the "correct" state, but this is not possible)


> I have tried to calculate oxygen K edge XAS in ice Ih. I built a 
> supercell and excite one of the oxygen.
> 
> To me, it seems that for HCH we set the 1s occupation number to be 1.5 
> (case.inc) and put the half electron in the background (case.inm). Then 
> why for FCH, we have to put the one electron in the valence band 
> (case.in2), not in the background this time? What is the difference 
> between they two?
> 
> I have attached part of my case.in2c file:
> TOT             (TOT,FOR,QTL,EFG,FERMI)
>       -9.0     512.0 0.50 0.05                EMIN, NE, ESEPERMIN, ESEPER0
> TETRA    0.000          (GAUSS,ROOT,TEMP,TETRA,ALL      eval)
>   0 0  1 0  1 1 -1 1  2 0  2 1 -2 1  2 2 -2 2  3 0  3 1 -3 1  3 2 -3 2  
> 3 3 -3 3  4 0  4 1 -4 1  4 2 -4 2  4 3 -4 3  4 4 -4 4  5 0  5 1 -5 1  5 
> 2 -5 2  5 3 -5 3  5 4 -5 4  5 5 -5 5  6 0  6 1 -6 1  6 2 -6 2  6 3 -6 3  
> 6 4 -6 4  6 5 -6 5  6 6 -6 6
>   0 0  1 0  1 1 -1 1  2 0  2 1 -2 1  2 2 -2 2  3 0  3 1 -3 1  3 2 -3 2  
> 3 3 -3 3  4 0  4 1 -4 1  4 2 -4 2  4 3 -4 3  4 4 -4 4  5 0  5 1 -5 1  5 
> 2 -5 2  5 3 -5 3  5 4 -5 4  5 5 -5 5  6 0  6 1 -6 1  6 2 -6 2  6 3 -6 3  
> 6 4 -6 4  6 5 -6 5  6 6 -6 6
>   0 0  1 0  1 1 -1 1  2 0  2 1 -2 1  2 2 -2 2  3 0  3 1 -3 1  3 2 -3 2  
> 3 3 -3 3  4 0  4 1 -4 1  4 2 -4 2  4 3 -4 3  4 4 -4 4  5 0  5 1 -5 1  5 
> 2 -5 2  5 3 -5 3  5 4 -5 4  5 5 -5 5  6 0  6 1 -6 1  6 2 -6 2  6 3 -6 3  
> 6 4 -6 4  6 5 -6 5  6 6 -6 6
>   0 0  1 0  1 1 -1 1  2 0  2 1 -2 1  2 2 -2 2  3 0  3 1 -3 1  3 2 -3 2  
> 3 3 -3 3  4 0  4 1 -4 1
> 
> Could you please tell me how to add the excited electron in the valence 
> band?
> 
> Best regards
> Jingyun
> 
> 
> 
> 
> 
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