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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 class="moz-cite-prefix">On 2020-12-11 19:25, Zahra Khatibi
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAA8vwQ45xUS1VB0j5ZAGF9rYFGCZN4VOH6NJgc021swV2WPzeQ@mail.gmail.com">
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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>
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<div><font size="2">Z. Khatibi</font></div>
<div><span
style="font-family:arial">School
of Physics</span><br>
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<div><span
style="font-family:arial;border-collapse:separate">Trinity
College Dublin<br>
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