<div dir="ltr">Hello, <div><br></div><div>Sure. I've shared the input and output in the following link:</div><div><a href="https://drive.google.com/drive/folders/1trdcWUw7GKSw0zLQouxygpaKwOl7_2KM?usp=sharing">https://drive.google.com/drive/folders/1trdcWUw7GKSw0zLQouxygpaKwOl7_2KM?usp=sharing</a></div><div><br></div><div>Kind regards,</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, Dec 12, 2020 at 5:01 PM Lorenzo Paulatto <<a href="mailto:paulatz@gmail.com" target="_blank">paulatz@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
  
    
  
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      <div dir="auto">
        <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>
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        <div dir="auto"><br>
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        <div dir="auto">All the best,</div>
        <div dir="auto">Zahra</div>
        <br>
        <br>
        <br>
        <br>
        <div class="gmail_quote" dir="auto">
          <div dir="ltr" class="gmail_attr">On Fri, Dec 11, 2020, 22:22
            Lorenzo Paulatto <<a href="mailto:paulatz@gmail.com" target="_blank">paulatz@gmail.com</a>> wrote:<br>
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            <div>
              <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>
              </div>
              <blockquote type="cite">
                <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">
                      <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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