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if you really want to know what happens close to gamma... look for
the theory of polaritons.<br>
also of interest can be to look for derivation of
Lyddane-Sachs-Teller relationship.<br>
stefano<br>
<br>
<br>
On 04/29/2011 12:23 PM, xirainbow wrote:
<blockquote
cite="mid:BANLkTikdZz6GY5FkuU8VpL64nSAt+29zgA@mail.gmail.com"
type="cite">
<pre wrap="">Dear Professor Eyvaz:
Thank you very much for your instruction:)
</pre>
<blockquote type="cite">
<pre wrap="">When q is zero, there is no longitude and transverse mode.
Really? How about optical modes? Did you pay attention to "O"?
</pre>
</blockquote>
<pre wrap="">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 ).
</pre>
<blockquote type="cite">
<pre wrap="">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,
<a class="moz-txt-link-abbreviated" href="mailto:isaev@ifm.liu.se">isaev@ifm.liu.se</a>, <a class="moz-txt-link-abbreviated" href="mailto:eyvaz_isaev@yahoo.com">eyvaz_isaev@yahoo.com</a>
------------------------------
*From:* xirainbow <a class="moz-txt-link-rfc2396E" href="mailto:nkxirainbow@gmail.com"><nkxirainbow@gmail.com></a>
*To:* PWSCF Forum <a class="moz-txt-link-rfc2396E" href="mailto:pw_forum@pwscf.org"><pw_forum@pwscf.org></a>
*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 <a class="moz-txt-link-rfc2396E" href="mailto:1009ukumar@gmail.com"><1009ukumar@gmail.com></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">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.
</pre>
<blockquote type="cite">
<pre wrap="">
</pre>
</blockquote>
<pre wrap="">
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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<pre wrap="">
--
____________________________________
Hui Wang
School of physics, Fudan University, Shanghai, China
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