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 <nkxirain...@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 -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110429/81926e79/attachment.htm