[QE-developers] R: Parallelization question for G-wise projector-wavefunctions product computation

[Marin Luca]

Dear Stefano,

Thanks a lot for the kind and fast reply! This is a good question, I also wondered that maybe the storage part was useless. I need this term because it enters the PAW equation for the "all-electron reconstruction" of the pseudopotential KS-states:

\psi_{ae} = \psi_{ps} + \sum_{R,l} [\phi_{R,l}^{ae} - \phi_{R,l}^{ps}] x <\beta_{R,l}|\psi_{ps}>

where R and l are the atomic species and projectors indices, \phi the "atomic-like" states from the PP calculation and \psi the KS state (there might be slight mistake in the formula).

If I now want to apply this correction to each of the u_{k+G} pw coefficients that contributes to \psi_{ps}, I think I also need the <\beta_{R,l}|\psi_{ps}> in a "G-wise" fashion, as I was naming it in the question.

I was therefore implementing this routine inside "gipaw", which already has precious stuff written for this PAW reconstruction.

I hope this gives you more information, and please let me know if you think there is already a good place either in pw or gipaw where to perform this!

Best,
Luca
ETH Zurich, PhD student
________________________________
Da: developers <developers-bounces at lists.quantum-espresso.org> per conto di Stefano de Gironcoli <degironc at sissa.it>
Inviato: sabato 8 febbraio 2025 15:55
A: developers at lists.quantum-espresso.org <developers at lists.quantum-espresso.org>
Oggetto: Re: [QE-developers] Parallelization question for G-wise projector-wavefunctions product computation


Dear Luca,

   the array betapsi_g(1:npw,1:nkb,1:nbnd) looks very big to me, unless the system is very small

   what do you need it for ? maybe one can compute the target quantity on the fly rather than storing this intermediate result


stefano


On 08/02/25 15:31, Marin Luca wrote:
Dear QE developers,
I had a conceptual question of how I should correctly modify a subroutine in order to avoid parallelization and memory’s absurdities. Specifically, my idea is to slightly modify one of the subroutines in the “calbec” (becmod.f90) interface that is computing <\Beta|\psi> products, and I am using QE v.6.4 because I’m working on a specific code repository using this version. By calling such or similar line:
CALL ZGEMV( 'C', npw, nkb, (1.0_DP,0.0_DP), beta, npwx, psi, 1, &
(0.0_DP, 0.0_DP), betapsi, 1 )
and subsequently summing through bands:
CALL mp_sum( betapsi( :, 1:m ), intra_bgrp_comm )
“calbec_k” computes the betapsi product as a 2D matrix with dimension (number of projectors, number of bands). My goal is to compute the same product but accessing the elements at each G vectors, i.e. without summing over the G vectors themselves. To this end, my (very basic, probably terrible) idea was to define another subroutine with an extra variable like this (without breaking the requirement of having unambiguous interface procedures in “calbec”):
calbec_k_modified ( npw, beta, psi, betapsi, betapsi_g, nbnd )
COMPLEX (DP), INTENT (out) :: betapsi_g(:,:,:)
and explicitly computing betapsi_g with nested do loops:
DO k = 1, npw
DO i = 1, nkb
DO j = 1, m
betapsi_g(k, i, j) = CONJG(beta(k, i)) * psi(k, j)
ENDDO
ENDDO
ENDDO
I am very unsure of whether this is a feasible approach and how I should handle the MPI parallelization in this case (I have little experience in QE development). I read the parallelization section of the developer’s manual, but I’m still quite confused. Any suggestions, critics or explanations will be very appreciated.
Best regards,
Luca Marin
ETH Zurich, PhD student





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