The ABINIT Users Mailing List ( CLOSED )

[Fabien Bruneval <fabien.bruneval@polytechnique.fr>]

Dear Philippe,

I'm maybe not the right person to answer. But, just rushing trough the 
new implementation (in version 5.4.2), it seems that the outputs of the 
subroutine findggp are not used anywhere in the following. The arrays 
gptab, gptabo, and ip2fp are built up and then their usage is everywhere 
commented out.

But, the scaling looks like N^3 where N is npweps, which is usually 
rather small (~100-500). It should not hit the calculation to much...

Matteo, can you tell your opinion on this?


Fabien



Philippe Blaise wrote:
> 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