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

[Paolo Giannozzi]

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>
>
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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, fax +39-0432-558222
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