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> >> *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 >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum at pwscf.org >> http://www.democritos.it/mailman/listinfo/pw_forum >> >> > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110429/bc08b9ab/attachment.htm
