[Pw_forum] negative phonon frequencies for 1-D polymer chain

[Ankit]

Thanks a lot Andrea. I just checked it and it solved the issue. 
Frequencies are all non-negative now.

Thank You,
Ankit Jain

On 04/14/2014 03:24 AM, Andrea Dal Corso wrote:
> Did you apply the 5.0.3 patch to QE 5.0.2? Without the patch, the phonon
> code gives wrong frequencies for some q points.
>
> HTH,
>
> Andrea
>
>
> On Mon, 2014-04-14 at 01:19 -0400, ankit jain wrote:
>> Hello Sanjeev,
>>
>> The pseudopotentials I am using are
>> H.pz-vbc.UPF<http://www.quantum-espresso.org/wp-content/uploads/upf_files/H.pz-vbc.UPF>
>>   and C.pz-vbc.UPF<http://www.quantum-espresso.org/wp-content/uploads/upf_files/C.pz-vbc.UPF>
>>
>>
>> Pseudopotential type: NORMCONS
>> Method: Von Barth-Car (direct fit)
>> Functional type: Perdew-Zunger (LDA) exch-corr
>> scalar relativistic
>>
>>
>> I have tried kgrid of 1*1*6 and 1*1*12, but both give negative frequencies.
>>
>>
>>
>> On Mon, Apr 14, 2014 at 12:18 AM, Sanjeev Gupta
>> <physics.skgupta at gmail.com>wrote:
>>
>>> what is kind of pseudopotential?
>>> How much k-point?
>>>
>>>
>>> wishes
>>> sanjeev
>>>
>>>
>>> On Sun, Apr 13, 2014 at 9:25 AM, Ankit <ankitjain.me.iitk at gmail.com>wrote:
>>>
>>>> Hello QE developers and users,
>>>>
>>>> I am trying to calculate phonon dispersion using ph.x and matdyn.x
>>>> routines of QE and I am stuck woth negative frequencies for a while now.
>>>>
>>>> I have a 1-D chain of polyethylene which has 6 atoms in the unit-cell.
>>>> The polymer chain is aligned in z-direction and I have added vacuum on
>>>> x- and y- direction. I did the structure relaxation and I am getting
>>>> total force after relaxtion as 0.000020, which I guess is sufficiently
>>>> small.
>>>>
>>>> After relaxation, when I am trying to calculate phonon dispersion using
>>>> ph.x and matdyn.x I am getting netting frequencies for some of the
>>>> phonon modes. I  searched online and on QE mailing list and tried couple
>>>> of different things:
>>>>
>>>> 1. The negative frequencies are appearing for non-gamma point as well,
>>>> so I guess its not a ASR issue. Anyway, I am using ASR but even after
>>>> this I am getting negative frequencies.
>>>> 2. I reduced my tr2_ph and conv_thr to 1.0d-14 and 1.0d-15 which I guess
>>>> are very small as suggested on QE FAQs.
>>>> 3. I checked phonon mode shapes for modes with negative frequencies and
>>>> they do not look like rotational mode.
>>>> 4. I tried changing number of k points from 6 to 12 in z direction but
>>>> this is also not the cause.
>>>>
>>>> I am really stuck here and not sure about the cause of negative
>>>> frequencies. With vc-relax, my structure is getting relaxed which I
>>>> guess means my structure is stable. But then I am not sure why I am
>>>> getting negative frequencies.
>>>>
>>>> I really appreciate any help or suggestions.
>>>>
>>>> Thanks,
>>>>
>>>> Ankit Jain
>>>> IIT Indore,
>>>> Indore,
>>>> India
>>>>
>>>>
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>>>>
>>>
>>>
>>> --
>>> With Best Regards,
>>>
>>> ------------------------------------
>>> Dr. Sanjeev Kumar Gupta
>>> Fulbright Post-Doctoral Scholar
>>> Dept. of Physics
>>> Michigan Technological University
>>> 1400 Townsend Drive, Houghton
>>> MI 49931, USA
>>> ------------------------------------
>>>
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