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    <div class="moz-cite-prefix">Hello Zahra,</div>
    <div class="moz-cite-prefix"><br>
    </div>
    <div class="moz-cite-prefix">why do you use PAW and 100Ry wfc
      cutoff?</div>
    <div class="moz-cite-prefix"><br>
    </div>
    <div class="moz-cite-prefix">Kind regards,</div>
    <div class="moz-cite-prefix"><br>
    </div>
    <div class="moz-cite-prefix">On 12/14/20 11:13 AM, Zahra Khatibi
      wrote:<br>
    </div>
    <blockquote type="cite"
cite="mid:CAA8vwQ69fpVRXX6D_D7vBc-465_g9EXcZWXxuTgbWWXuDzBjtA@mail.gmail.com">
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      <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"
            moz-do-not-send="true">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" moz-do-not-send="true">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">
          <div> <br>
            <blockquote type="cite">
              <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>
              </div>
            </blockquote>
            <p><br>
            </p>
            <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>
            </p>
            <p>cheers<br>
            </p>
            <p><br>
            </p>
            <blockquote type="cite">
              <div dir="auto">
                <div dir="auto"><br>
                </div>
                <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"
                      moz-do-not-send="true">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">
                    <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
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                                                      <div dir="ltr">
                                                        <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>
                                                      </div>
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                                                  </div>
                                                </div>
                                              </div>
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    </blockquote>
    <p><br>
    </p>
    <pre class="moz-signature" cols="72">-- 
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

=======================================================

E-mail: <a class="moz-txt-link-abbreviated" href="mailto:tobias.kloeffel@fau.de">tobias.kloeffel@fau.de</a></pre>
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