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<div dir="auto">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.</div>
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<p>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</p>
<p><br>
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<p>cheers<br>
</p>
<p><br>
</p>
<blockquote type="cite"
cite="mid:CAA8vwQ7qGCdW7Pq-P+v47NGFRkOTd7uX2mhbqHBpGbvt8c-4gA@mail.gmail.com">
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<div dir="auto">All the best,</div>
<div dir="auto">Zahra</div>
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<div dir="ltr" class="gmail_attr">On Fri, Dec 11, 2020, 22:22
Lorenzo Paulatto <<a href="mailto:paulatz@gmail.com"
moz-do-not-send="true">paulatz@gmail.com</a>> wrote:<br>
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<p>Hello Zahra,</p>
<p>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.</p>
<p>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. <br>
</p>
<p><br>
</p>
<p>cheers<br>
</p>
<div>On 2020-12-11 19:25, Zahra Khatibi wrote:<br>
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<div dir="ltr">Dear all,
<div><br>
</div>
<div>First of all, I hope everyone is safe and well in
these crazy times. </div>
<div>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). </div>
<div>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? </div>
<div>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. </div>
<div><br>
</div>
<div>Kind regards,</div>
<div>
<div dir="ltr" data-smartmail="gmail_signature">
<div dir="ltr"><span
style="color:rgb(136,136,136)">--</span><br
style="color:rgb(136,136,136)">
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<div><font size="2">Z.
Khatibi</font></div>
<div><span
style="font-family:arial">School
of Physics</span><br>
</div>
<div><span
style="font-family:arial;border-collapse:separate">Trinity
College Dublin<br>
</span></div>
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