[QE-users] phonon dispersion relation from the full IFCs

[jqhuang16b at imr.ac.cn]

Thank you so much, professor. I really appreciate your scrupulous reply over and over again.
In the QE code(subroutine rgd_dyn) of computing the rigid-ion (long-range) term, it is commented that
"Only the G-space term is implemented: the Ewald parameter alpha must be large enough to have negligible r-space contribution".
But in the following value assignment, alph= 1.0d0, not a very large number. 
I think such a value will not make the real-space term vanish in the Ewald summation.
How to understand this?


> -----原始邮件-----
> 发件人: "Lorenzo Paulatto" <paulatz at gmail.com>
> 发送时间: 2020-01-10 17:19:48 (星期五)
> 收件人: users at lists.quantum-espresso.org
> 抄送: 
> 主题: Re: [QE-users] phonon dispersion relation from the full IFCs
> 
> > Is it equivalent to the regular adopted Ewald summation method in mathematics?
> 
> I think you forgot to attach the paper in question...
> 
> That said, if there is not lo-to splitting, there are no effectiv 
> charges and no long-range interaction. Than there is no problem doing 
> Fourier interpolation.
> 
> 2D is a bit special, but the QE code has special techniques to deal with 
> 2D phonon interpolation, I think it is explained in Phys. Rev. B 94, 085415
> 
> cheers
> 
> > 
> > With thanks and best regards !
> > Happy New Year !
> > 
> > 
> > --
> > Jian-qi Huang
> > 
> > Magnetism and Magnetic Materials Division
> > Institute of Metal Research
> > Chinese Academy of Sciences
> > 72 Wenhua Road, Shenyang 110016, China
> > 
> > email:jqhuang16b at imr.ac.cn
> > 
> >> -----原始邮件-----
> >> 发件人: "Lorenzo Paulatto" <paulatz at gmail.com>
> >> 发送时间: 2020-01-09 03:56:21 (星期四)
> >> 收件人: users at lists.quantum-espresso.org
> >> 抄送:
> >> 主题: Re: [QE-users] phonon dispersion relation from the full IFCs
> >>
> >>> Thank you for reply, professor. I understand the regular routine
> >>> implemented in QE where the long-range contribution is added in
> >>> reciprocal space. My point is can I get the correct dynamical matrix
> >>> just by making inverse Fourier transformation of the full(short+long)
> >>> IFCs in a large real space?
> >>>
> >>
> >> The dynamical matrix at Gamma is discontinuity with respect to the
> >> points nearby, which would make any Fourier transform impossible to
> >> converge.
> >>
> >> I think you should explain WHY you want to do this, and you may get some
> >> better answer.
> >>
> >> In practice, if I was obliged at gunpoint, I would replace the dynamical
> >> matrix file at Gamma (typically dyn1) with one computed very close to
> >> Gamma, let's say q=0.001,0,0. Edit the file to trick q2r into thinking
> >> that it was done at exactly Gamma, and see was comes out.
> >>
> >> If the material has a non-analytic term (i.e. the long range term
> >> depends on the direction), this will definitely not work. Otherwise, you
> >> may get something decent.
> >>
> >>
> >> cheers
> >>
> >>
> >>
> >> -- 
> >> Lorenzo Paulatto - Paris
> >> _______________________________________________
> >> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
> >> users mailing list users at lists.quantum-espresso.org
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> 
> -- 
> Lorenzo Paulatto - Paris
> _______________________________________________
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