[QE-users] pp.x calculation very slow

[Paolo Giannozzi]

Your supercell is small but you have a high cutoff and a large number of
k-points, which makes the overall computational load quite heavy. Moreover
your choice of parallelization is less than optimal: you should use both
k-point and plane-wave parallelization, something like "mpirun -np 160 pw.x
-nk 16" or so. For reference: I ran your Fe.pw.scf.in input in 20' on a
small 36-core machine with two (powerful) GPU's. The nscf calculation took
1h20' for the calculation and is taking as much time if not more to write
the files. Also note that not all postprocessing calculations are optimized
for large runs.

Paolo

On Mon, Mar 15, 2021 at 7:23 PM Lenz Fiedler <fiedler.lenz at gmail.com> wrote:

> (resent because something went wrong with the header line)
>
> Hi users,
>
> I am experiencing a problem with pp.x. I want to calculate the LDOS for a
> 16 Fe atom supercell using a 560 value energy grid and the 3D grid given by
> the DFT calculation (100x100x100 grid points). I have performed the DFT
> calculation by first doing a SCF calculation (8x8x8 k-points) and then a
> non-SCF calculation (14x14x14 k-points) successfully. Now I am trying to
> do:
>
> mpirun -np 160 pp.x -in Fe.pp.ldos.in
>
> but the calculation takes way longer than I anticipated. The entire DFT
> calculation took less than a day, while for the LDOS, after about 12 hours,
> only 20 tmp files had been written. Am I doing something wrong? Or is this
> expected? At this rate, calculating the LDOS would take days, which is why
> I am assuming I am doing something wrong.
> Please find my output and input files here:
>
>
> https://drive.google.com/drive/folders/1R-m5jlw1bcNxe3nBXjc4dms-IoMMp4Ir?usp=sharing
> (the pp.out file is from a run where I investigated if a lower number of
> CPUs helps, but that was slower, as expected.)
>
> Kind regards
> Lenz
>
> PhD Student (HZDR / CASUS)
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 206, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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