[Pw_forum] LO-TO splitting in dynmat.x

[xirainbow]

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(黄良锋) DFT and phonon physics
> ======================================================================
> Add: Research Laboratory for Computational Materials Sciences,
> Instutue of Solid State Physics,the Chinese Academy of Sciences,
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-- 
____________________________________
Hui Wang
School of physics, Fudan University, Shanghai, China
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