[Pw_forum] Phonon branch enumeration

[Stefano Baroni]

On Mar 11, 2009, at 1:32 PM, Jeffrey Mullen wrote:

>
> Thanks for the recommendation. I have performed the calculation with  
> the
> iverbosity set to 1. It will take me a while to parse it and  
> understand
> the output, but if I can figure out the relationships, I will  
> attempt to
> code the ordering into the application.

that would be really great!
SB

>
>
> Cheers
> Jeff Mullen
> North Carolina State University
>
>
> Dal Corso Andrea wrote:
>
>>
>> It is an interesting idea. I think it is possible to make the
>> symmetry classification of the displacements patterns with the same
>> routine that makes the symmetry classification of the eigenvectors
>> of the dynamical matrix. Presently, this is not done. You can
>> code this feature yourself or just use iverbosity=1. With this option
>> the code writes the displacement patterns and you can
>> check their symmetry.
>>
>> Andrea
>>
>>
>>
>>
>>
>>> Cheers
>>> Jeff
>>>
>>>
>>>
>>> e kb wrote:
>>>
>>>
>>>
>>>> Dear Jeff,
>>>> I am definitely not an expert on the topic but I'd like to  
>>>> understand
>>>> your question better.
>>>>
>>>>   Mode symmetry, D_6h(6/mmm) point group:
>>>>
>>>>   omega(  1 -  1) =        -37.4  [cm-1]   --> A_2u            I
>>>>   omega(  2 -  3) =        -33.9  [cm-1]   --> E_1u            I
>>>>   omega(  4 -  4) =        863.3  [cm-1]   --> B_2g
>>>>   omega(  5 -  6) =       1336.0  [cm-1]   --> E_2g
>>>>
>>>> So you have the irr. representations and the values for omega  
>>>> (values
>>>> are printed with higher precision in the previous part after
>>>> diagonalization as you reported). What exactly do you want to know
>>>> more (that you cannot check from a book on group theory) ?
>>>>
>>>> Emine Kucukbenli, grad. student, SISSA, Italy.
>>>>
>>>> --- On *Tue, 3/10/09, Jeffrey Mullen /<jtmullen at ncsu.edu>/* wrote:
>>>>
>>>>   From: Jeffrey Mullen <jtmullen at ncsu.edu>
>>>>   Subject: [Pw_forum] Phonon branch enumeration
>>>>   To: pw_forum at pwscf.org
>>>>   Date: Tuesday, March 10, 2009, 2:34 AM
>>>>
>>>> Greetings
>>>>
>>>> I am testing electron-phonon interaction calculations with  
>>>> graphene and
>>>> have encountered a problem enumerating the resulting phonon  
>>>> branches.
>>>> When I run the ph.x calculation at the q(0 0 0), the code  
>>>> calculates 4
>>>> representations:
>>>>
>>>>   Representation #  1 modes #   1  2
>>>>   Representation #  2 mode #   3
>>>>   Representation #  3 mode #   4
>>>>   Representation #  4 modes #   5  6
>>>>
>>>>
>>>> When the values for omega are calculated, the results are:
>>>>
>>>> **************************************************************************
>>>>   omega( 1) =      -1.119851 [THz] =     -37.354451 [cm-1]
>>>>   omega( 2) =      -1.016557 [THz] =     -33.908905
>>>> [cm-1]
>>>>   omega( 3) =      -1.016557 [THz] =     -33.908905 [cm-1]
>>>>   omega( 4) =      25.882237 [THz] =     863.344237 [cm-1]
>>>>   omega( 5) =      40.051667 [THz] =    1335.988701 [cm-1]
>>>>   omega( 6) =      40.051667 [THz] =    1335.988701 [cm-1]
>>>> **************************************************************************
>>>>
>>>>
>>>> with the following mode symmetries:
>>>>
>>>>   Mode symmetry, D_6h(6/mmm) point group:
>>>>
>>>>   omega(  1 -  1) =        -37.4  [cm-1]   --> A_2u            I
>>>>   omega(  2 -  3) =        -33.9  [cm-1]   --> E_1u            I
>>>>   omega(  4 -  4) =        863.3  [cm-1]   --> B_2g
>>>>   omega(  5 -  6) =       1336.0  [cm-1]   --> E_2g            R
>>>>
>>>>
>>>> My question is one of ordering. How do I extract which omega(##)
>>>> corresponds to which representation/mode?
>>>>
>>>> Thanks
>>>> Jeff Mullen
>>>> North Carolina State
>>>> University
>>>>
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>>>>
>>>>
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) /  
stefanobaroni (skype)

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