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

[jqhuang16b at imr.ac.cn]

Thank you for the detailed answer, professor.
---"I think you should explain WHY you want to do this, and you may get some better answer."
The reason I want to do so is because I have read one paper which adopts the full IFCs to reproduce the phonon dispersion perfectly. Moreover, the result shows there is no LO-TO splitting at Gamma point in the 2D case, which agrees with the theoretical prediction of optical dispersion for 2D materials. This is really intresting for me, but I am unable to judge its reasonableness. I have attached the paper for the reference.
 
Now my confusion about the treatment of the dipole-dipole interaction is why not deal with the long-range dynamical contribution by making inverse Fourier transform just the same way as short-range contribution, given that the formula of long-range IFCs is already available(X. Gonze et al, PRB 50. 13035 (1994)). Is it equivalent to the regular adopted Ewald summation method in mathematics?

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
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