The ABINIT Users Mailing List ( CLOSED )

[Philippe Blaise <philippe.blaise@cea.fr>]

Since a few days I'm benchmarking the parallel performances of abinit 5.4.2
for my GW calculations.

Contrary to the 'sigma' part of the calculation, the 'screening' part 
seems to be
very inefficient in parallel (~50 cpus / ZrO2 / 500 bands, 20-30 Ha for 
the cutoffs),
and it is mainly due to the loop on the Gi, Gj pairs done in the FINDGGP 
subroutine.
This loop computes indexes during hours ! Its complexity seems to be in 
O(N^4) where
N is the number of Gi i=1,...,N.

For the moment, I have decided to comment this loop and to do an 
unconditionnal
return, as if they were no symmetry to take into account.
This is of course a work-around, but it's far more efficient in parallel,
even if there is more matrix elements to compute for chi0 (approx a 
factor of 2 of 3 times).

Nevertheless I see a comment in the file findggp.F90

! TODO Calculate SG outside the loop, requires more memory but should be 
faster!

that sounds good to me. Will it be implemented in a next version ?

Of course, any comment from the GW experts/developpers is welcome.

Regards,

 Philippe