[QE-users] pp.x calculation very slow

[Lenz Fiedler]

Dear Professor Giannozzi,

So if I understand you correctly, you did something like

mpirun -np 18 pp.x -in Fe.pp.ldos.in

on the nscf data wirh 14x14x14 and got the 560 cube files in 30 minutes?
This is what I would expect/hope for as well. I will try this and if I
cannot reproduce it there might be something wrong with my installation.

Kind regards
Lenz


Am So., 21. März 2021 um 16:31 Uhr schrieb Paolo Giannozzi <
p.giannozzi at gmail.com>:

> 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
>>>> 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
>>>
>>> _______________________________________________
>>> 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
>
> _______________________________________________
> 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
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