[QE-developers] Incompatible FFT grid in ph.x calculation

[Paolo Giannozzi]

Six significant digits should be sufficient for all cases (in your case,
they are, after a small change to the code I recently made). Wyckoff
positions are the safest way to provide  positions with the correct
symmetry.

Paolo

On Fri, Aug 14, 2020 at 4:15 PM Xiao Zhang <xiaozha at umich.edu> wrote:

> Dear Paolo,
>
> I see. Thanks for checking this and I will try what you suggested. So in
> general is there a good number of digits that we should shoot for? Or is it
> more system dependent, and we just need to play around it?
>
> Thanks!
> Best!
> Xiao
>
> On Fri, Aug 14, 2020 at 9:37 AM Paolo Giannozzi <p.giannozzi at gmail.com>
> wrote:
>
>> I see: it's the usual problem with "almost-symmetric" coordinates. If you
>> transform the "almost 1/3" and "almost 2/3" into something closer to 1/3
>> and 2/3 in the x and y atomic coordinates, the error disappears. In the
>> previous version of the code, the checks were done  in a slightly different
>> way and this problem did not show up.
>>
>> Paolo
>>
>> On Fri, Aug 14, 2020 at 3:22 PM Paolo Giannozzi <p.giannozzi at gmail.com>
>> wrote:
>>
>>> On Fri, Aug 14, 2020 at 2:51 PM Xiao Zhang <xiaozha at umich.edu> wrote:
>>>
>>> I realized that in 6.6, an additional line shows: Fft bands division:
>>>> nmany = 1 (line 15). Not sure if this means anything or not?
>>>>
>>>
>>> it doesn't.
>>>
>>> Apparently the check on fractional translations being commensurate with
>>> the real-space grid is a little bit too strict. Not sure how to fix it in a
>>> safe way, though
>>>
>>> Paolo
>>>
>>>
>>>> Thanks!
>>>> Best!
>>>> Xiao
>>>>
>>>> On Fri, Aug 14, 2020 at 8:31 AM Paolo Giannozzi <p.giannozzi at gmail.com>
>>>> wrote:
>>>>
>>>>> It would be useful to see the scf output for v.6.5 as well
>>>>>
>>>>> Paolo
>>>>>
>>>>> On Fri, Aug 14, 2020 at 9:14 AM Xiao Zhang <xiaozha at umich.edu> wrote:
>>>>>
>>>>>> Dear QE developers,
>>>>>>
>>>>>> I'm sending the email asking about an error I get from the phonon
>>>>>> calculations in the 6.6 version of quantum espresso. I'm trying to run
>>>>>> phonon calculation for 2H SiC and have the scf run finished with no
>>>>>> problem, but when I run phonon calculation following that, I received an
>>>>>> incompatible FFT grid error. This happened only with the new version of QE
>>>>>> while using the exact same input, QE 6.5 works fine and provides output. I
>>>>>> was wondering if this is something we expect? (I do realize there is one
>>>>>> potentially relevant tag on the release note under "fixed")
>>>>>>
>>>>>> I attached one example just in case it might help: This is 2H-SiC and
>>>>>> I attached the input and output from scf, input and output from ph.x from
>>>>>> both 6.5 and 6.6. The k-points and cutoffs are reduced for quick tests, but
>>>>>> converged k-points and cutoffs show the same issue. The structure is
>>>>>> relaxed within QE, and the PP used is ONCV-PBE. I'm a bit confused why this
>>>>>> is seen in phonon calculation but not the scf calculation? I assumed that
>>>>>> if it's a problem of my input structure, I should've seen a problem in
>>>>>> both? Any hint or suggestions would be very helpful!
>>>>>>
>>>>>> Thanks a lot!
>>>>>> Best!
>>>>>> Xiao Zhang
>>>>>> Department of Materials Science and Engineering
>>>>>> University of Michigan, Ann Arbor
>>>>>>
>>>>>> _______________________________________________
>>>>>> developers mailing list
>>>>>> developers at lists.quantum-espresso.org
>>>>>> https://lists.quantum-espresso.org/mailman/listinfo/developers
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
>>>>> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
>>>>> Phone +39-0432-558216, fax +39-0432-558222
>>>>>
>>>>>
>>>
>>> --
>>> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
>>> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
>>> Phone +39-0432-558216, fax +39-0432-558222
>>>
>>>
>>
>> --
>> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
>> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
>> Phone +39-0432-558216, fax +39-0432-558222
>>
>>

-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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