[Pw_forum] LO-TO splitting in dynmat.x

[Stefano de Gironcoli]

if you really want to know what happens close to gamma... look for the 
theory of polaritons.
also of interest can be to look for derivation of Lyddane-Sachs-Teller 
relationship.
stefano


On 04/29/2011 12:23 PM, xirainbow wrote:
> Dear Professor Eyvaz:
> Thank you very much for your instruction:)
>
>> When q is zero, there is no longitude and transverse mode.
>> Really? How about optical modes? Did you pay attention to "O"?
>>
> I do not express myself clearly.
> When q=0,  q has no direction. Therefore, optical modes can not be
> classified into longitude or transverse ones. As a result, at q=0,  these
> optical phonon should be still degenerate( LO=TO ).
>
>
>
>> Bests,
>> Eyvaz.
>>
>> -------------------------------------------------------------------
>> Prof. Eyvaz Isaev,
>> Department of Physics, Chemistry, and Biology (IFM), Linkoping University,
>> Sweden
>> Theoretical Physics Department, Moscow State Institute of Steel&  Alloys,
>> Russia,
>> isaev at ifm.liu.se, eyvaz_isaev at yahoo.com
>>
>>
>> ------------------------------
>> *From:* xirainbow<nkxirainbow at gmail.com>
>> *To:* PWSCF Forum<pw_forum at pwscf.org>
>> *Sent:* Fri, April 29, 2011 9:30:31 AM
>>
>> *Subject:* Re: [Pw_forum] LO-TO splitting in dynmat.x
>>
>> Dear Sonu Kumar
>> What you said is reasonable;)
>>
>> I have two little questions.
>> One:
>> Does LO-TO splitting must disappear at the boundary of Brillouin zone?
>>
>> Two:
>> I can understand the LO-TO splitting near Gamma point.
>> However, at Gamma point(not  near Gamma point), q=0. When q is zero, there
>> is no longitude and transverse mode. Why are there LO-TO splitting at Gamma
>> point?
>>
>> Thanks:)
>>
>>
>>
>> On Fri, Apr 29, 2011 at 1:21 PM, sonu kumar<1009ukumar at gmail.com>  wrote:
>>
>>> Dear All QE users,
>>>
>>> i am sorry again, as i havn't corrected the subject title.
>>>
>>>
>>> (2) only cubic crystals has LO and TO braches.
>>> crystals ( having considerable values of macroscopic dielectric constant [
>>> i suppose
>>> epsilon infinity] and born effective charges, as pointed  out by Prof.
>>> Eyvaz Isaev) with low symmetry can, also, have LO-TO splitting. But this can
>>> be  different in different symmetry directions, so one has to search all
>>> symmetry directions for this splitting.
>>>
>>> For cubic crystals splitting is equal in all directions.
>>>
>>> with regards,
>>>
>>> --
>>> Sonu Kumar
>>>
>>> Phd Student
>>> Physics Department
>>> Indian Institute of Technology
>>> Delhi-110016, India
>>> web:-http://www.iitd.ac.in/
>>>
>>> _______________________________________________
>>> Pw_forum mailing list
>>> Pw_forum at pwscf.org
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>>>
>>
>> --
>> ____________________________________
>> Hui Wang
>> School of physics, Fudan University, Shanghai, China
>>
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>>
>
>
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