[Pw_forum] xspectra calculation (wumindt2)

[wumindt2]

Dear Matteo, 

It seems i have found the problem. It's not the problem of the 
xcoordcrys. I set it as .true. and the polarization vectors are (0,0,1) and
(0,1,0). The xray k vector is the default value (1,0,0).
BTW, can we use the same vector for polarization and xay k moment? 
e.g. Both of them are (1,0,0). Is it OK?

The problem i found is that i set the "cut_occ_states" = .true.
Then it cut all the occupied state that i expected to see.
When i reset it to .false., i saw the expected peak. 

I have another problem, what does the "ef_r" do in the calculation?
For instance, i got fermi level of -5 eV with scf calculation.
The i set ef_r= -5/13.6 Ry. Then, in the calculated xspectra data, where is
the Fermi level? It is ajusted to 0 eV, or still is the -5 eV?

Sorry to bother you again.
Thanks so much.

Cheers,

Min Wu 2010-10-18



>From: Matteo Calandra <matteo.calandra at impmc.jussieu.fr>
>Reply-To: PWSCF Forum <pw_forum at pwscf.org>
>To: pw_forum at pwscf.org
>Subject: Re:[Pw_forum] xspectra calculation (wumindt2)
>Date: Mon, 18 Oct 2010 09:35:10 +0200
>
>dear Min Wu,
>
>  the attachment do not go through the pw_forum, so I cannot
>do much about it. What I can tell you is that we calculate
>Co and LiCoO2 and we get a good agreement with experiments.
>Maybe you can try to compare with the following paper:
>
>Juhin et al. Phys. Rev. B 81, 115115 (2010)
>http://link.aps.org/doi/10.1103/PhysRevB.81.115115
>
>Anyway, from four message what seems to be wrong (assuming the scf
>run to be correct) are the unit of the polarization vector
>(assuming you're dealing with the dipolar part only and assuming
>the peak you're referring to is dipolar). Did you set xcoordcrys to
>the proper value (see below)?
>
>For zhqt concerns CoO2, note that the pre-edge
>of CoO2 at the Co K-edge has a quadrupolar part, so if you stick
>to the dipolar calculation you want be able to reproduce the pre-edge 
>peak. Note also that in the case of LiCoO2, which is probably
>not so different from yours, DFT fails in the
>pre-edge and you have to use DFT+U.
>
>In particular, remember that if you don't set the variable
>xcoordcrys=.false. your xepsilon and xkvec are in reduced coordinates.
> From Doc/INPUT_XSPECTRA
>
>xkvec(1:3)        real(DP) 
>DEFAULT=(1.0,0
>.0,0.0)
>                   coordinates of the x-ray momentum k
>
>
>xepsilon(1:3)     real(DP) 
>DEFAULT=(1.0,0
>.0,0.0)
>                   coordinates of the incident x-ray
>                   polarization vector
>
>xcoordcrys        logical 
>DEFAULT=.true.
>                   .true. to use crystal coordinates for
>                   k and epsilon
>
>
>Maybe you could try to reproduce our calculation on LiCoO2 so that
>you are sure of not having any errors with the input file.
>The paper is very detailed so you can compare every step in the calculation.
>
>All the best, M.
>
> >Message: 6
> >Date: Mon, 18 Oct 2010 05:03:50 +0800
> >From: "wumindt2"

> >Subject: Re: [Pw_forum] Xspectra calculation (wumindt2)
> >To: pw_forum at pwscf.org
> >Message-ID:

> >Content-Type: text/plain; charset="gb2312"
>
> >Dear Matteo,
>
> >I met some problem when calculating the XASs with the Xspectra.
> >I tested the example of quartz, and got the consistent result with the
> >published work.
> >Then i moved on to test another example of solid CO2, which has an 
> >isotropic
> >symmetry according to C. Brouder's paper. But the X-ray absorption 
> >spectrum
> >i got was totally wrong. The first sharp peak which is well-known 
> >existing
> >in CO2 was not found.
> >We also tested a single CO2 molecule which is still a clear-cut >example.
> >The C atom and the two O atoms are all in the Z axis. So the 
> >polarization vectors
> >of (0,0,1) and (1,0,0) are enough for this case. However, we still 
> >cannot get the
> >right XAS. To make it easier for you to understand my problem, I 
> >attached the input files of this calculation.
> >The GIPAW pseudopotentials i used were downloaded from the website of >QE.
>
> >Thanks a lot for the help.
>
> >Best regards,
>
> >Min Wu
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