the electristatic interaction at the origin of LO-TO splitting is always present...
for any q<>0 (even very small) it is included in the calculation. in the limit of q->0 in non-metallic systems it gives origin to a non analytic behavior that must be calculate separately. If you want to Fourier interpolate the phonon dispersions calculated on a regular grid of q-points you are in trouble because non analyticity of the phonon dispersion implyes long-range (1/R^3) interatomic force constants and so you need to 1) evaluate Z* and epsilon_infty in the limit of q->0 that determine the non-analyticity 2) remove from dynamical matrix in every q point in you grid an electrostatic model that gives the correct non-analyticity for q->0 and is smooth elsewhere 3) Fourier interpolate the modified (hopefully short-range) dynamical matrices 4) add back the model in any q-point you want to study. This is what the sequence ph.x -> q2r.x -> matdyn.x does (in example06 for instance) thete is some discussion of these issues in Review of Modern Physics 73, 515 (2001) and in Phys Rev 43, 7231 (1991) stefano On 04/29/2011 05:05 AM, xirainbow wrote: > Dear Eyvaz: > Thank you very much;) > >> Is there LO-TO splitting far away from Gamma point? >> No. >> > Does LO-TO splitting must disappear at the boundary of Brillouin zone? > > > > _______________________________________________ > 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/20110429/093d10e5/attachment.htm
