<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:times new roman,new york,times,serif;font-size:12pt">Dear Wang,<br><br>Let me reiterate: LO-TO splitting takes place ONLY at the Gamma point. Why? <br>It is the physics. Please read at least the review paper I mentioned in my previous mail.<br>Or take a good textbook.<br><br><div class="gmail_quote"><div>>For cubic crystals splitting is equal in all directions.<br></div></div>So, for non-cubic LO-TO splitting also occurs and the splitting is different for different directions. That is <br>why one can see a discontinuity near the Gamma point in phonon dispersion relations. <br><br>>When q is zero, there is no longitude and transverse mode. <br>Really? How about optical modes? Did you pay attention to "O"? <br><br>Bests,<br>Eyvaz.
<br><div> </div>-------------------------------------------------------------------<br>Prof. Eyvaz Isaev, <br>Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden <br>Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, <br>isaev@ifm.liu.se, eyvaz_isaev@yahoo.com<div><br></div><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><br><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><font face="Tahoma" size="2"><hr size="1"><b><span style="font-weight: bold;">From:</span></b> xirainbow <nkxirainbow@gmail.com><br><b><span style="font-weight: bold;">To:</span></b> PWSCF Forum <pw_forum@pwscf.org><br><b><span style="font-weight: bold;">Sent:</span></b> Fri, April 29, 2011 9:30:31 AM<br><b><span style="font-weight: bold;">Subject:</span></b> Re: [Pw_forum] LO-TO splitting in dynmat.x<br></font><br>
<div>Dear Sonu Kumar</div><div>What you said is reasonable;)</div><div><br></div><div>I have two little questions.</div><div>One:</div><div><span style="font-family: arial,sans-serif; font-size: 12.5px; border-collapse: collapse;">Does LO-TO splitting must disappear at the boundary of Brillouin zone?</span></div>
<div><br></div><div>Two:</div><div>I can understand the LO-TO splitting near Gamma point.</div><div>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?</div>
<div><br></div><div>Thanks:)</div><div><br></div><br><br><div class="gmail_quote">On Fri, Apr 29, 2011 at 1:21 PM, sonu kumar <span dir="ltr"><<a rel="nofollow" ymailto="mailto:1009ukumar@gmail.com" target="_blank" href="mailto:1009ukumar@gmail.com">1009ukumar@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">Dear All QE users,<br><br>i am sorry again, as i havn't corrected the subject title.<div><br><br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">(2) only cubic crystals has LO and TO braches.<br></blockquote>
<div> </div></div><div class="gmail_quote"><div>crystals ( having considerable values of macroscopic dielectric constant [ i suppose<br>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.<br>
<br>For cubic crystals splitting is equal in all directions.<br></div></div><br>with regards,<br clear="all"><font color="#888888"><br>-- <br>Sonu Kumar<br><br>Phd Student<br>Physics Department<br>Indian Institute of Technology <br>
Delhi-110016, India<br><span>
web:-<a target="_blank" href="http://www.iitd.ac.in/">http://www.iitd.ac.in/</a></span><br>
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<br></blockquote></div><br><br clear="all"><br>-- <br>____________________________________<br>Hui Wang<br>School of physics, Fudan University, Shanghai, China<br>
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