[QE-users] time consuming band structure calculation for a supercell

[Zahra Khatibi]

Hello,

Sure. I've shared the input and output in the following link:
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> 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> 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
>>
>> _______________________________________________
>> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
>> users mailing list users at lists.quantum-espresso.orghttps://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
>
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.orghttps://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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20201214/78810c71/attachment.html>