[QE-users] time consuming band structure calculation for a supercell
Tobias Klöffel
tobias.kloeffel at fau.de
Mon Dec 14 11:18:25 CET 2020
Hello Zahra,
why do you use PAW and 100Ry wfc cutoff?
Kind regards,
On 12/14/20 11:13 AM, Zahra Khatibi wrote:
> Hello,
>
> Sure. I've shared the input and output in the following link:
> https://drive.google.com/drive/folders/1trdcWUw7GKSw0zLQouxygpaKwOl7_2KM?usp=sharing
> <https://drive.google.com/drive/folders/1trdcWUw7GKSw0zLQouxygpaKwOl7_2KM?usp=sharing>
>
> Kind regards,
>
> On Sat, Dec 12, 2020 at 5:01 PM Lorenzo Paulatto <paulatz at gmail.com
> <mailto:paulatz at gmail.com>> wrote:
>
>
>> Aslo I have tried running the band calculation on different
>> systems (local pc with 12 nodes) and HPC (with 36 and 72 nodes).
>> Every time I have the same problem. I have tried QE 6.5 and 6.4
>> for this calculation all with same issue.
>
>
> For comparison, I have here a calculation with 119 electrons, 10
> k-points, 100 Ry kinetic energy cutoff. One SCF iteration takes
> about 5 seconds on 32 CPUs (2 nodes of a very old computing
> cluster that has since been retired). From 120 to 190 electrons
> there should be around a factor 4 of CPU times. But it would be
> easier to say which is the source of the discrepancy if you sent
> your input and output files to teh list, to have a look
>
>
> cheers
>
>
>>
>> All the best,
>> Zahra
>>
>>
>>
>>
>> On Fri, Dec 11, 2020, 22:22 Lorenzo Paulatto <paulatz at gmail.com
>> <mailto:paulatz at gmail.com>> wrote:
>>
>> Hello Zahra,
>>
>> if I understand correctly, you manage to do the scf
>> calculation, but then the band calculation is very slow. The
>> cost per k-point of nscf should be more or less the same as
>> the cost per k-point of one scf iteration. If it is not,
>> there is something wrong. One possible problem, is that
>> ecutwfc is interpreted differently during nscf. A tight value
>> (1.d-12 or less) may cause the threshold of diagonalization
>> in nscf to become too small and very slow to converge. This
>> should be fixed in v 6.7, but you can just increase ecutwfc
>> in nscf if you're using a previous version.
>>
>> If not, it may be a problem with parallelism, i.e. running on
>> too many CPUs or some proper human error like running with
>> all the processes on the same computing node.
>>
>>
>> cheers
>>
>> On 2020-12-11 19:25, Zahra Khatibi wrote:
>>> Dear all,
>>>
>>> First of all, I hope everyone is safe and well in these
>>> crazy times.
>>> I'm calculating the electronic band dispersion of a 2D
>>> heterostructure with a 59 atom unit cell. This system is a
>>> small bandgap (10-20 meV) semiconductor. The number of
>>> valence bands is (valence electrons/2) 181. When I set
>>> 'nbnd' to 190, the band structure calculation costs me 30
>>> minutes for each k point on HPC with 72 processors. This
>>> means that if I do a simple band calculation for a high
>>> symmetry path with 100 points within, I have to wait almost
>>> 50 hours! This even becomes worst when I try to evaluate the
>>> band dispersion with SOC switched on (twice the spin
>>> degenerate band calculation).
>>> Since the band dispersion evaluation is the major part of
>>> our study, I was wondering if there is a way around this
>>> problem, like reducing the number of bands by only looking
>>> at energy interval close to Fermi energy?
>>> I could see that there are lots of papers and studies in the
>>> literature with huge unit cells and heavy atoms that have
>>> presented numerous band structures (using QE). So I really
>>> appreciate it if you could help me here.
>>>
>>> Kind regards,
>>> --
>>> Z. Khatibi
>>> School of Physics
>>> Trinity College Dublin
>>>
>>> _______________________________________________
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--
M.Sc. Tobias Klöffel
=======================================================
HPC (High Performance Computing) group
Erlangen Regional Computing Center(RRZE)
Friedrich-Alexander-Universität Erlangen-Nürnberg
Martensstr. 1
91058 Erlangen
Room: 1.133
Phone: +49 (0) 9131 / 85 - 20101
=======================================================
E-mail: tobias.kloeffel at fau.de
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