[QE-users] pp.x calculation very slow

[Lenz Fiedler]

Dear Professor Giannozzi,

Thank you so much for your answer. You are right, I did not really think
about the parallelization for the initial SCF calculation, I was more
puzzled by the pp.x calculation. If I understand you correctly, using
something like "pp.x -nk 16" might also help speed up the LDOS calculation
as well? But there also might be an upper limit of how fast this performs
and it could be that I simply have to wait a while to obtain the LDOS? As
in, except for my suboptimal parallelization strategy, the long runtime of
pp.x I observed was not due to wrong usage but simply to computational load
of the problem?

Kind regards
Lenz Fiedler

PhD Student (HZDR / CASUS)


Am Di., 16. März 2021 um 16:36 Uhr schrieb Paolo Giannozzi <
p.giannozzi at gmail.com>:

> 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
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
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