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 <[email protected]
<mailto:[email protected]>> 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 <[email protected]
<mailto:[email protected]>> 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
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