[Pw_forum] LO-TO splitting in dynmat.x

[Eyvaz Isaev]

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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