<div dir="ltr">Dear Stefano,<div><br></div><div>Thank you very much for your prompt response, that helps a lot!</div><div>I will repeat the tests as you suggested but it's good to know that my system is behaving normally and I can then proceed with more complex calculations.</div><div><br></div><div>All the best,</div><div>Martina</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Apr 24, 2018 at 3:23 AM, Stefano de Gironcoli <span dir="ltr"><<a href="mailto:degironc@sissa.it" target="_blank">degironc@sissa.it</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
  
    
  
  <div bgcolor="#FFFFFF" text="#000000">
    <p><tt>Dear Martina Lessio,</tt></p>
    <p><tt>   first of all I would say that a convergence error of 1.d-5
        Ry in a 6 atom cell looks pretty much converged to me. I think
        that even your ecutrho = 240 Ry calculation (~1.d-5 Ry per atom)
        looks quite good.<br>
      </tt></p>
    <p><tt>   coming to the way things converge:</tt></p>
    <p><tt>   - total energy convergence with respect to ecutwfc is
        expected to be from above </tt><tt><tt>because of variational
          principle</tt>: the higher ecutwfc is the more planewaves are
        included in the wavefunction expansion, hence the lower the
        energy. However in the ultrasoft pseudopotential definition the
        energy is not only a function of the wavefunctions but also
        includes a dependence on augmentation charges, that are
        localized and may contain higher Fourier components with respect
        to 4*ecutwfc ( = 240 in your case). Failing to include enough
        Fourier components in the augmentation charges will affect a
        number of integrals but not in a variational way... integrals
        would simply be inaccurate and the inaccuracy can be both from
        above or from below.<br>
      </tt></p>
    <p><tt>   - I would perform cutoff convergence test in a slightly
        different order: 1) I would check convergence of total energy
        (and stress, and forces) as a function of ecutwfc using the
        default value for ecutho=4*ecutwfc (that is without specifying
        ecutrho in the input). When this procedure converges (and it can
        initially converge from below due to augmentation charge Fourier
        components being missing) this means that wavefunction expansion
        AND augmentation-charge expansion are both converged. 2) I would
        then fix ecutrho=4*converged_ecutwfc, which takes care of
        augmentation charge convergence, and I would check whether I can
        get away with a lower ecutwfc for the wavefunction expansion.<br>
      </tt></p>
    <p><tt>    - as for k-point sampling convergence, there is no
        variational principle w.r.t. number of k-points: it's again a
        matter of convergence of an integral. The denser the grid the
        better the integral but there is no variational principle with
        respect to which k-point you include and which you dont.</tt></p>
    <p><tt>  hope this helps<br>
      </tt></p>
    <p><tt>stefano</tt><br>
    </p><div><div class="h5">
    <br>
    <div class="m_-3203274337787247819moz-cite-prefix">On 24/04/2018 05:56, Martina Lessio
      wrote:<br>
    </div>
    </div></div><blockquote type="cite"><div><div class="h5">
      <div dir="ltr">Dear Quantum Espresso community,
        <div><br>
        </div>
        <div>I am new to Quantum Espresso and I am trying to run some
          simple simulations on MoTe2 bulk. Unfortunately I seem to be
          having some issues with some preliminary convergence tests
          for charge density cutoff and K-point grid and I am hoping to
          get some help from you on this.</div>
        <div>Here is a graph with the results of the charge density
          cutoff convergence test I performed while setting the kinetic
          energy cutoff equal to 60 Ry (I performed a test to set this
          as well):</div>
        <div><img src="cid:part1.2D2DD99A.A75EBD52@sissa.it" width="545" height="327"><br>
          I am worried about these results because I would expect the
          total energy to go down rather than going up when I increase
          ecutrho. I also observe a similar energy trend when I increase
          the k-point grid, which also seems unusual and possibly wrong
          to me.</div>
        <div>I am copying below the input I have used for these
          calculations and I would greatly appreciate any help with
          figuring our whether I am doing something wrong.</div>
        <div><br>
        </div>
        <div>Thank you so much!</div>
        <div><br>
        </div>
        <div>Kind Regards,</div>
        <div>Martina Lessio</div>
        <div>
          <div><br>
          </div>
          <div class="m_-3203274337787247819gmail_signature">
            <div dir="ltr">
              <div dir="ltr">
                <div>Postdoctoral Research Scientist</div>
                <div>Department of Chemistry</div>
                <div>Columbia University</div>
                <br>
                <p><span style="font-variant-ligatures:no-common-ligatures"> &control</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> 
                      calculation = 'scf'</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> 
                      restart_mode='from_scratch',</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> 
                      prefix='MoTe2_ecutwfc',</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> 
                      pseudo_dir =
                    '/home/mlessio/espresso-5.4.0/<wbr>pseudo/',</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> 
                      outdir='/home/mlessio/<wbr>espresso-5.4.0/tempdir/'</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> /</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> &system</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> 
                      ibrav= 4, A=3.530, B=3.530, C=13.882, cosAB=-0.5,
                    cosAC=0, cosBC=0,</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> 
                      nat= 6, ntyp= 2,</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> 
                      ecutwfc =60.0 ecutrho=300.</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> 
                      nspin =4, lspinorb =.true., noncolin=.true.</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> /</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> &electrons</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> 
                      mixing_mode = 'plain'</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> 
                      mixing_beta = 0.7</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> 
                      conv_thr =  1.0d-8</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> /</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures">ATOMIC_SPECIES</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> Mo 
                    95.96 Mo.rel-pbe-spn-rrkjus_psl.1.0.<wbr>0.UPF</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> Te 
                    127.6 Te.rel-pbe-n-rrkjus_psl.1.0.0.<wbr>UPF</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures">ATOMIC_POSITIONS
                    {crystal}</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures">Te
                        0.333333334         0.666666643        
                    0.625000034</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures">Te
                        0.666666641         0.333333282        
                    0.375000000</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures">Te
                        0.666666641         0.333333282        
                    0.125000000</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures">Te
                        0.333333334         0.666666643        
                    0.874999966</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures">Mo
                        0.333333334         0.666666643        
                    0.250000000</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures">Mo
                        0.666666641         0.333333282        
                    0.750000000</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"></span><br>
                </p>
                <p><span style="font-variant-ligatures:no-common-ligatures">K_POINTS
                    {automatic}</span></p>
                <p><span style="font-variant-ligatures:no-common-ligatures"> 
                    8 8 2 0 0 0</span></p>
              </div>
            </div>
          </div>
        </div>
      </div>
      <br>
      <fieldset class="m_-3203274337787247819mimeAttachmentHeader"></fieldset>
      <br>
      </div></div><pre>______________________________<wbr>_________________
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<a class="m_-3203274337787247819moz-txt-link-freetext" href="https://lists.quantum-espresso.org/mailman/listinfo/users" target="_blank">https://lists.quantum-<wbr>espresso.org/mailman/listinfo/<wbr>users</a></pre>
    </blockquote>
    <br>
  </div>

<br>______________________________<wbr>_________________<br>
users mailing list<br>
<a href="mailto:users@lists.quantum-espresso.org">users@lists.quantum-espresso.<wbr>org</a><br>
<a href="https://lists.quantum-espresso.org/mailman/listinfo/users" rel="noreferrer" target="_blank">https://lists.quantum-<wbr>espresso.org/mailman/listinfo/<wbr>users</a><br></blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr">Martina Lessio, Ph.D.<div>Frontiers of Science Lecturer in Discipline</div><div>Postdoctoral Research Scientist</div><div>Department of Chemistry</div><div>Columbia University</div></div></div></div></div>
</div>