[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 

>When q is zero, there is no longitude and transverse mode. 
Really? How about optical modes? Did you pay attention to "O"?  


Prof. Eyvaz Isaev, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, 

Theoretical Physics Department, Moscow State Institute of Steel & Alloys, 

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.
Does LO-TO splitting must disappear at the boundary of Brillouin zone?

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?


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 
>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
>Pw_forum mailing list
>Pw_forum at pwscf.org

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