[Pw_forum] Difference in total energies (serial vs parallel) for calculations with hybrid functional using norm conserving pseudopotential: Possible bug

[Paolo Giannozzi]

On Tue, Aug 29, 2017 at 7:30 AM, Prasenjit Ghosh <prasenjit.jnc at gmail.com>
wrote:

Paolo, is there some quick fix for the bug?
>

no, it's a tricky bug. Or maybe there is one: in my tests, the problem
seems to disappear if you replace your structure (lattice only, positions
are ok)

&system  ibrav= 0 , celldm(1)= 8.81679607, ... /
 CELL_PARAMETERS (alat)
   0.999861009  -0.000000000  -0.000000000
  -0.499930505   0.865905034  -0.000000000
  -0.000000000  -0.000000000   3.428582875

with the equivalent structure

&system   ibrav= 4 , celldm(1)= 8.8155706147, celldm(3)=3.42905948, ... /

Why, I don't know

Paolo


> With regards,
>
> Prasenjit
>
> On 28 August 2017 at 21:17, Paolo Giannozzi <p.giannozzi at gmail.com> wrote:
>
>> There is a problem with reduced-cutoff calculations (using ecutfock <
>> 4*ecutwfc) and k-points. Thank you for reporting this
>>
>> Paolo
>>
>> On Mon, Aug 28, 2017 at 8:33 AM, Prasenjit Ghosh <prasenjit.jnc at gmail.com
>> > wrote:
>>
>>> Dear all,
>>>
>>> We are doing calculations for my system (PbI2) with hybrid functionals
>>> (using the ACE algorithm) and norm conserving pseudopotentials. Presently
>>> we are performing this calculations using scalar relativistic
>>> non-conserving pseudopotentials for Pb and I. The pseudopotentials have
>>> been generated by me using PBE functionals. I have tested these (at the
>>> level of GGA) and it can reproduce well the lattice parameters and
>>> electronic bandstructure of a range of different compounds (from metallic
>>> Pb to ionic PbI2 and CsPbBr3).
>>>
>>> When we perform the hybrid calculations using GAU-PBE, we find that the
>>> total energy differs when we use 1 core and 4 cores. The energy difference
>>> is about 0.23 Ry. However, for both the cases, the standard GGA-PBE
>>> calculations give same results (total energy). Even the band gap with
>>> GAU-PBE (using 1 and 4 cores) are same. A look into the output file
>>> suggests that the difference comes from
>>> -averaged Fock potential + Fock energy.
>>>
>>> Since I have generated the pseudopotential, I thought that there might
>>> be some issue with this. Hence to cross check, I downloaded the
>>> normconserving pseudopotentials for Pb and I from
>>> http://theossrv1.epfl.ch/Main/Pseudopotentials (pbe.0.3.1.tgz). For
>>> these two pseudopotentials also the total energies (1 core vs 4 cores)
>>> differ. The input files, pseudopotential files and the output files can be
>>> downloaded from the link given below:
>>>
>>> http://www.iiserpune.ac.in/~pghosh/QE/
>>>
>>> These results are reproducible on different machines, using different
>>> compilers (eg. gfortran vs intel).
>>>
>>> I think that there is a bug in the code, particularly the part where the
>>> contributions to total energy from EXX is collected. If the developers can
>>> suggest where exactly to look for in the code, I can give it a try to sort
>>> it out.
>>>
>>> With regards,
>>>
>>> Prasenjit.
>>>
>>> --
>>> PRASENJIT GHOSH,
>>> IISER Pune,
>>> Dr. Homi Bhabha Road, Pashan
>>> Pune, Maharashtra 411008, India
>>>
>>> Phone: +91 (20) 2590 8203 <+91%2020%202590%208203>
>>> Fax: +91 (20) 2589 9790 <+91%2020%202589%209790>
>>>
>>> _______________________________________________
>>> Pw_forum mailing list
>>> Pw_forum at pwscf.org
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>>>
>>
>>
>>
>> --
>> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
>> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
>> Phone +39-0432-558216 <+39%200432%20558216>, fax +39-0432-558222
>> <+39%200432%20558222>
>>
>>
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>>
>
>
>
> --
> PRASENJIT GHOSH,
> IISER Pune,
> Dr. Homi Bhabha Road, Pashan
> Pune, Maharashtra 411008, India
>
> Phone: +91 (20) 2590 8203 <+91%2020%202590%208203>
> Fax: +91 (20) 2589 9790 <+91%2020%202589%209790>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum
>



-- 
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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