[QE-developers] questions and possible bug on exx calculations

[Paolo Giannozzi]

On Sat, Mar 28, 2020 at 7:51 PM Morales-Silva, Miguel A. <
moralessilva2 at llnl.gov> wrote:

The augmentation functions in real space (e.g. tabxx(ia)%qr(...)) do not
> depend on the specific k-points of the orbital pair densities being
> augmented. This, I believe, is incorrect. The phase factor coming from
> (xkp-xkq) is added in addusxx_g, but not in addusxx_r.
>

The phase in G-space, exp[i(k-k')\tau] I guess, comes from the structure
factor that translates the augmentation function at the atomic position.
There is something not right in the current real-space expression: the
augmentation term as it is written now seems to be periodic, while the rest
has a exp[i(k-k')*r] dependence

Paolo


> best,
>
> *************************************
> Miguel A. Morales
> Quantum Simulations Group, Physics Division
> Lawrence Livermore National Laboratory
> phone: 925-423-4956
> *************************************
>
> ------------------------------
> *From:* developers <developers-bounces at lists.quantum-espresso.org> on
> behalf of Lorenzo Paulatto <paulatz at gmail.com>
> *Sent:* Saturday, March 28, 2020 10:00 AM
> *To:* developers at lists.quantum-espresso.org <
> developers at lists.quantum-espresso.org>
> *Subject:* Re: [QE-developers] questions and possible bug on exx
> calculations
>
> I add to what already said by Paolo
>
> >  1. On routines PAW_newdxx and PAW_xx_energy, the code is only executed
> >     on ionode which I believe is a bug when k-point and/or band
> >     parallelization is used.
>
> The code is only executed in ionode, and the result added into
> deexx,later on in exx.f90 there is
>
> IF (okvan) THEN
>      CALL mp_sum( deexx(:,ii), intra_egrp_comm )
> ENDIF
>
> Which means that if we compute that part on all CPUs, the contribution
> would be multiplied by the number of CPUs. It would be better to majke
> PAW_newdxx parallel, but as it is inexpensive I did not bother. Bugs are
> always possible. Same story of PAW_xx_energy, which is added to energy,
> which is then summed over all CPUs
>      CALL mp_sum( energy, inter_egrp_comm )
>      CALL mp_sum( energy, intra_egrp_comm )
>      CALL mp_sum( energy, inter_pool_comm )
>
>
>
> >  2.  From what I see, tqr=.true. is not implemented for exx routines
> >     when k-points are used.
>
> It is implemented. To clarify: there is a part of code that is common to
> PAW and Ultrasoft, this part depends on the value tqr and is computed by
> either newdxx_r or newdxx_g. Than there is a part which is paw-only,
> which does not depends on the value of tqr; this is computed by
> PAW_newdxx. Also note that when okpaw=.true. also okvan is true.
>
>
> >     The phases of the pair densities need be
> >     added, probably inside addusxx_r for this to be correct. In a
> >     handful of cases I've tested, I get significantly different results
> >     with/without tqr with hybrid functionals and kpoints. Gamma point or
> >     single kpoint runs, of course, is fine. It would probably be better
> >     to perform a runtime check and abort if necessary.
>
> There are probably some bugs in that part, but not what you think.
> Actually as the PAW specific part is identical with and without tqr, I
> would suspect the bug is in the Ultrasoft code.
>
>
> cheers#
> --
> Lorenzo Paulatto - Paris
> _______________________________________________
> developers mailing list
> developers at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/developers
> _______________________________________________
> 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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/developers/attachments/20200330/baa96347/attachment.html>