[Pw_forum] Xspectra calculation (wumindt2)

[wumindt2]

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
2010-10-17


>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, 11 Oct 2010 10:08:16 +0200
>
>Dear
>
>  I assume you are talking of the dipolar part only.
>For the quadrupolar it is substantially more complicate.
>The number of independent calculations that you have
>to perform to obtain the isotropic cross section (powder)
>depends on the  point group of the space group
>of your crystal.
>It is 1 for a cubic or tetraedric crystal,
>2 for a uniaxial crystal and it is 3, 4, 6 for a biaxial
>(ot trichroic) crystal.
>I suggest you read
>C. Brouder J. Phys.: Condens. Matter 2 (1990) 701-738
>for more details.
>
>M.
>
>
>> 
>> Message: 3
>> Date: Sat, 09 Oct 2010 22:48:53 +0800
>> From: "wumindt2"

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

>> Content-Type: text/plain;	charset="gb2312"
>> 
>> Dear matteo,
>> 
>> Thanks. 
>> 
>> For dichroism compound, do we just need the in-plane and the c-axis
>> polarization vectors? 
>> While for trichroism compound, do we need to calculate three different
>> polarization vectors?
>> Am i right?
>> 
>> Best regards,
>> 
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