[Pw_forum] LO-TO splitting in dynmat.x

[xirainbow]

Dear Professor Stefano:
You mean when q->0, the polar phonon is described by Huang-equation?
If so, I know the answer:)
Thank you very much;)

On Fri, Apr 29, 2011 at 7:16 PM, Stefano de Gironcoli <degironc at sissa.it>wrote:

>  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> <nkxirainbow at gmail.com>
> *To:* PWSCF Forum <pw_forum at pwscf.org> <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> <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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