[Pw_forum] Phonon calculation

[Vincenzo Verdolino]

Dear all,

Thanks for all your hints. Xhang, I had this feeling too and I did give a try to different version. At the end i managed to have no imaginary frequency. I am not 100% sure but it might be possible that sampling K-points with offset (i.e. 12 12 12 1 1 1) was giving troubles. Moreover i have increased up to 15 15 15 sampling with no offset. This is the kind of case where one belives to be converged (energy ok, structure ok etc) but you are not and phonon analysis tells you!

Now I stll have to fix a couple of issues becaus the soft modes Around gamma seems to be not perfectly linear wereas acustic should but this coud be a q-mash issue

I will keep u up to date

Vincenzo

Sent from my iPhone

> On 25/ago/2014, at 16:25, Xiaolong Zhang <xlzhang.iop at gmail.com> wrote:
> 
> Dear Vincenzo Verdolino,
> 
> Same problem here, and this could be version dependent. I tested a system with D3d symmetry. The QE4.3 and QE 5.1 give perfect phonon
> dispersion, but with QE5.0.x there is always small imaginary frequencies around a high symmetric point (but not Gamma), you may try with
> latest QE or with some older one (like 4.3). Hope this helps.
> 
> 
> 
>> On Mon, Aug 25, 2014 at 7:04 PM, Vincenzo Verdolino <vincenzo.verdolino at gmail.com> wrote:
>> I have personally tested several things...PW cutoff, k sampling fft mash...everything...the only missing thing is the phonon tr2 value...i am doing that right now and let you know
>> 
>> Vincenzo
>> 
>> Sent from my iPhone
>> 
>>> On 25/ago/2014, at 12:51, "jzlhubei at gmail.com" <jzlhubei at gmail.com> wrote:
>>> 
>>> I have the similar problem with QE calculation with Phonon, I can not reproduece the result of an article for negative frequency around Gamma.
>>> But I think that the tr2_ph to be 1.0d-14 is enough.
>>> and recently I found Blog talks abount this question for negative frequency. BUt I can not get the idea why.I hope some senior user can give insight
>>> comment on this question
>>> the Blog web is http://blog.sina.com.cn/s/blog_5f15ead20101rhyj.html
>>> 
>>> jzlhubei at gmail.com
>>>  
>>> From: Vincenzo Verdolino
>>> Date: 2014-08-25 17:05
>>> To: dalcorso; PWSCF Forum
>>> Subject: Re: [Pw_forum] Phonon calculation
>>> Hi Andrea,
>>> 
>>> 
>>> thank you for your answer, i will do that and give you updates if things get better.
>>> 
>>> Vincenzo  
>>> 
>>> 
>>>> On Mon, Aug 25, 2014 at 10:40 AM, Andrea Dal Corso <dalcorso at sissa.it> wrote:
>>>> I would start checking convergence with respect to tr2_ph.
>>>> 
>>>> HTH,
>>>> 
>>>> Andrea
>>>> 
>>>> 
>>>> 
>>>> On Mon, 2014-08-25 at 07:25 +0200, Vincenzo Verdolino wrote:
>>>> > _______________________________________________
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>>>> 
>>>> --
>>>> Andrea Dal Corso                    Tel. 0039-040-3787428
>>>> SISSA, Via Bonomea 265              Fax. 0039-040-3787249
>>>> I-34136 Trieste (Italy)             e-mail: dalcorso at sissa.it
>>>> 
>>>> 
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> 
> 
> -- 
> Xiao-Long Zhang
> 
> Ph.D student,
> Institute of Physics, 
> Chinese Academy of Sciences
> 8 Nansanjie, Zhongguancun
> Beijing 100190, China
> Email:  xlzhang at iphy.ac.cn OR xlzhang.iop at gmail.com
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