[Pw_forum] Pw_forum Digest, Vol 40, Issue 19

[matteo calandra]

Dear Min Wu,

   I think you should sit down a bit and try to solve this issue
by yourself. This is not a problem concerning the code as you would have
the same problem with any other code, but it concerns basic
physics and group theory.
In the future we plan to write a program to find the isotropic cross section
with the sallest number of calculations possible from the knowledge of
the symmetries of the lattice.
However this is not yet done (I am not aware of any program doing this).

So, as I always do in these case, you should si down,try to understand
Ch. Bouder's paper and find the polarization vectors necessary to
obtain the isotropic cross section.

M.

>
> Message: 6
> Date: Tue, 12 Oct 2010 14:59:33 +0800
> From: "wumindt2" <wumindt2 at zju.edu.cn>
> Subject: Re: [Pw_forum] Xspectra calculation (wumindt2)
> To: pw_forum at pwscf.org
> Message-ID: <CTFHHDRTTMMZGMEUQITYAFBYXCPW.wumindt2 at zju.edu.cn>
> Content-Type: text/plain;	charset="gb2312"
>
> Dear Matteo,
>
> Thanks for the information, i read the C. Brouder the paper a little bit.
> I'am still not sure how to choose the polarization vector.
> For instance, we have a crystal with spacegroup of P42/MNM, point  
> group of 4/mmm.
> According to the Table in C. Brouder's paper, this is a dichroism compound.
> Thus, how can we choose the polarization vector when calculating the XAS
> of this compound?
> Can you please show me how?
>
> Thanks so much!
>
> Cheers,
>
> Min Wu
> 2010-10-12
>
>
>> 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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> End of Pw_forum Digest, Vol 40, Issue 19
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