[Pw_forum] how to obtained the eigndisplacement by eignvector in PWSCF

[Stefano Baroni]

On Jun 6, 2006, at 7:04 AM, Varadharajan Srinivasan wrote:

> Hello,
>
> Please correct me if I am wrong but to obtain the eigenvectors of  
> the dynamical matrix the values given by the code which are  
> actually the normalized eigen displacements cannot be directly  
> used. For this purpose I usually modify the code to print out the  
> unnormalized eigen displacements and then multiply each component  
> with the sqaure root of the corresponding mass.

I do not remember whether the code outputs eigen-vectors of the  
dynamical matrix or eigen-displacements. In the latter case (which, I  
understand, is what you assume), you do not have to do anything in  
order to obtain displacement patterns. In the second (which, if my  
memory does not fail is more likely), you have to multiply eigen- 
vectors components by the square root of the atomic masses in order  
to obtain atomic displacement pattern.

In any event, it seems to me that your distinction between  
"normalized" and "unnormalized" eigen-anything is somewhat  
misleading. Only the _direction_ of atomic displacement patterns  
actually matters, and the direction is, by its very definition,  
independent on normalization.

> The mass is taken in Rydberg units. In these units the electron  
> mass is 1/2.

Again, a change in the mass units would not change the direction of  
the eigen-displacements nor the relation between eigen-displacements  
and eigen-vectors of the dynamical matrix. It would affect the  
calculated frequencies, though.

Stefano

>
> Best,
> Vardha.
>
>
> On Tue, 6 Jun 2006, Stefano Baroni wrote:
>
>> I do not quite get the question.
>> It is the mass of Pb as found in any perdiodic table: 207.2 amu  
>> (see www.webelements.com)
>>
>> Atomic masses should also be specified in the "ATOMIC_SPECIES"  
>> card whose format, in the present case, should be something like:
>>
>> Pb 207.2 Pb_pseudopotential_file_name
>>
>> Are you confused instead by the negative value of the frequency?  
>> (this has nothing to do with masses)
>>
>> Hope this helps - Stefano
>>
>> On Jun 5, 2006, at 4:23 PM, 针叶 朱 wrote:
>>
>>> Dear all user:
>>> i have calculated the phonon of PbTiO3, and i have obtained  
>>> eignvector of atom under each mode.
>>> for example:
>>>   omega( 1) =      -4.221301 [THz] =    -140.808368 [cm-1]
>>>  ( -0.092855  0.000000 -0.004178  0.000000  0.001020  0.000000 )
>>>  ( -0.185613  0.000000 -0.008352  0.000000  0.002040  0.000000 )
>>>  (  0.598322  0.000000  0.026924  0.000000 -0.005371  0.000000 )
>>>  (  0.598322  0.000000  0.021990  0.000000 -0.006576  0.000000 )
>>>  (  0.488678  0.000000  0.026924  0.000000 -0.006576  0.000000 )
>>>     now i have kown the eigndisplacement  |u> = M^(-1/2) | v>.
>>> but i am confused with mass M. for example, for Pb atom in  
>>> PbTiO3. how much is mass of Pb in equation above?
>>> please grive me some construction!
>>> Regards
>>>                                            zhuzhenye
>>> 抢注雅虎免费邮箱-3.5G容量，20M附件！
>>
>> ---
>> Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
>> Trieste
>> [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)
>>
>> Please, if possible, don't  send me MS Word or PowerPoint attachments
>> Why? See:  http://www.gnu.org/philosophy/no-word-attachments.html
>>
>>
>>

---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
[+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)

Please, if possible, don't  send me MS Word or PowerPoint attachments
Why? See:  http://www.gnu.org/philosophy/no-word-attachments.html



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