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

[Stefano Baroni]

1.0 tons is 1000000000 times larger than 1.0 mg. A very large number indeed! SB

--
Stefano Baroni, Trieste -- swift message written and sent on the go

> On 10 Jan 2020, at 18:03, jqhuang16b at imr.ac.cn wrote:
> 
> 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
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>> 
>> -- 
>> 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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> _______________________________________________
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