[QE-users] pp.x calculation very slow

[Paolo Giannozzi]

A LDOS calculation should take more or less the same time as the
calculation of the charge density, plus reading, wroting, etc.. I just
tried and it took half an hour on 18 processors (CPU cores, not GPUs)

Paolo

On Wed, Mar 17, 2021 at 5:26 PM Lenz Fiedler <fiedler.lenz at gmail.com> wrote:

> 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)
>>> _______________________________________________
>>> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
>>> users mailing list users at lists.quantum-espresso.org
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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)
>> users mailing list users at lists.quantum-espresso.org
>> https://lists.quantum-espresso.org/mailman/listinfo/users
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users



-- 
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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