[Pw_forum] LO-TO splitting in dynmat.x

[xirainbow]

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/
>>
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>>
>
>
> --
> ____________________________________
> Hui Wang
> School of physics, Fudan University, Shanghai, China
>
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>


-- 
____________________________________
Hui Wang
School of physics, Fudan University, Shanghai, China
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