[Pw_forum] LO-TO splitting in dynmat.x
Eyvaz Isaev
eyvaz_isaev at yahoo.com
Fri Apr 29 09:41:54 CEST 2011
Dear Wang,
Let me reiterate: LO-TO splitting takes place ONLY at the Gamma point. Why?
It is the physics. Please read at least the review paper I mentioned in my
previous mail.
Or take a good textbook.
>For cubic crystals splitting is equal in all directions.
So, for non-cubic LO-TO splitting also occurs and the splitting is different
for different directions. That is
why one can see a discontinuity near the Gamma point in phonon dispersion
relations.
>When q is zero, there is no longitude and transverse mode.
Really? How about optical modes? Did you pay attention to "O"?
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
>http://www.democritos.it/mailman/listinfo/pw_forum
>
>
--
____________________________________
Hui Wang
School of physics, Fudan University, Shanghai, China
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