Dear Professor Stefano: You mean when q->0, the polar phonon is described by Huang-equation? If so, I know the answer:) Thank you very much;)
On Fri, Apr 29, 2011 at 7:16 PM, Stefano de Gironcoli <degironc at sissa.it>wrote: > if you really want to know what happens close to gamma... look for the > theory of polaritons. > also of interest can be to look for derivation of Lyddane-Sachs-Teller > relationship. > stefano > > > > On 04/29/2011 12:23 PM, xirainbow wrote: > > Dear Professor Eyvaz: > Thank you very much for your instruction:) > > > When q is zero, there is no longitude and transverse mode. > Really? How about optical modes? Did you pay attention to "O"? > > > 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 ). > > > > > 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> <nkxirainbow at gmail.com> > *To:* PWSCF Forum <pw_forum at pwscf.org> <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> > <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 listPw_forum at > pwscf.orghttp://www.democritos.it/mailman/listinfo/pw_forum > > -- > ____________________________________ > Hui Wang > School of physics, Fudan University, Shanghai, China > > _______________________________________________ > Pw_forum mailing listPw_forum at > pwscf.orghttp://www.democritos.it/mailman/listinfo/pw_forum > > > _______________________________________________ > Pw_forum mailing listPw_forum at > pwscf.orghttp://www.democritos.it/mailman/listinfo/pw_forum > > > > _______________________________________________ > 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/20110429/16189fb3/attachment-0001.htm