Dear Huang: Thanks very much for your valuable discussion. I are reading your mentioned paper:)
On Fri, Apr 29, 2011 at 5:20 PM, lfhuang <lfhuang at theory.issp.ac.cn> wrote: > Dear Wang, H: > > Suppose a uniaxial crystal(no cubic): c>a=b. Suppose there is a > > double-degenerate polar E_u mode, in which all atoms move in the a-b > plane. > > If the wavevector around Gamma point is in the a-b plane, the degenerate > E > > mode will split into LO and TO mode. > > Am I right? > > It is probable for some ionic crystals, but still depends. > Maybe the Equ. 98 (nonanalytic part of the dynamical matrix) in Rev. Mod. > Phys. 73, 515 (2001) by prof. S. Baroni etc. and the related parts in the > book "Dynamical Theory of Crystal Lattices" by M. Born & K. Huang can give > you much information if these things are important/interesting to you. > > In addition, is the method "finite difference" you mentioned exactly the > "frozen phonon" or "small displacement" method? If so, the treatment like > that in PWSCF should be good to obtain a satisfied LO/TO splitting, although > honestly I haven't done this in the "frozen phonon" method. Some people > propose other methods, like using a prolonged supercell, which I think, > could not fully describe the long-range dipolar interaction, because of its > long-range character (as prof. Stefano de Gironcoli said ~1/R^3). > > Best Wishes! > Yours Sincerely > L. F. Huang > ------ > ====================================================================== > L.F.Huang(???) DFT and phonon physics > ====================================================================== > Add: Research Laboratory for Computational Materials Sciences, > Instutue of Solid State Physics,the Chinese Academy of Sciences, > P.O.Box 1129, Hefei 230031, P.R.China > Tel: 86-551-5591464-326(office) > Fax: 86-551-5591434 > Our group: http://theory.issp.ac.cn > ====================================================================== > > _______________________________________________ > 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/bd58dee3/attachment.htm
