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    <p><tt>Dear Martina Lessio,</tt></p>
    <p><tt>  the 8*ecutwfc is a rule of thumb that is indeed often
        suggested for US pseudopotential.</tt></p>
    <p><tt>  There is nothing special in the factor 8, it simply
        reflects the expectation that </tt><tt><tt>augmentation charges
          typically contain more Fourier components than the 4*ecutwfc
          coming from the square of the wavefuncitons. <br>
        </tt>
      </tt></p>
    <p><tt> </tt></p>
    <p><tt>   As you did the converge test and found that 55/280 Ry are
        good in your case it should be ok to use these values.</tt></p>
    <p><tt>   best,<br>
      </tt></p>
    <p><tt>stefano</tt><br>
    </p>
    <br>
    <div class="moz-cite-prefix">On 25/04/2018 22:11, Martina Lessio
      wrote:<br>
    </div>
    <blockquote type="cite"
cite="mid:CAGco_WQw8zW=daF9N9+1DkH20Ek3Bo5Ys6kxUZ-3ju3V7yOxEA@mail.gmail.com">
      <div dir="ltr">Dear Stefano,
        <div><br>
        </div>
        <div>I have one more question regarding the convergence tests. I
          have performed the tests in the order that you recommended and
          found that if I set ecutrho=280 Ry I can get away with
          ecutwfc=55 Ry without negatively impacting the convergence. So
          I am thinking of using these parameters for my future
          calculations. However, I have read in many QE resources that
          if you use ultrasoft pseudopotentials like I do, ecutrho
          should be at least equal to 8*ecutwfc. So I am now wondering
          whether it is an issue that in my case ecutrho is only equal
          to about 5*ecutwfc or given that I performed the recommended
          convergence tests it is okay to have this setup even for
          pseudopotentials.</div>
        <div><br>
        </div>
        <div>I hope my question is clear.</div>
        <div>Thanks so much!</div>
        <div><br>
        </div>
        <div>All the best,</div>
        <div>Martina</div>
        <div><br>
        </div>
        Martina Lessio<br>
        Postdoctoral Research Scientist<br>
        Department of Chemistry<br>
        Columbia University
        <div><br>
        </div>
      </div>
      <div class="gmail_extra"><br>
        <div class="gmail_quote">On Tue, Apr 24, 2018 at 10:53 AM,
          Martina Lessio <span dir="ltr"><<a
              href="mailto:ml4132@columbia.edu" target="_blank"
              moz-do-not-send="true">ml4132@columbia.edu</a>></span>
          wrote:<br>
          <blockquote class="gmail_quote" style="margin:0 0 0
            .8ex;border-left:1px #ccc solid;padding-left:1ex">
            <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">
              <div>
                <div class="h5"><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"
                        moz-do-not-send="true">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="m_6004932123691587237h5"> <br>
                            <div
                              class="m_6004932123691587237m_-3203274337787247819moz-cite-prefix">On
                              24/04/2018 05:56, Martina Lessio wrote:<br>
                            </div>
                          </div>
                        </div>
                        <blockquote type="cite">
                          <div>
                            <div class="m_6004932123691587237h5">
                              <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:part3.DDF4FFC2.2F17DDA3@sissa.it"
                                    class="" 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_6004932123691587237m_-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/espresso<wbr>-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>
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                          <pre>______________________________<wbr>_________________
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                      <br>
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                    </blockquote>
                  </div>
                  <br>
                  <br clear="all">
                  <div><br>
                  </div>
                </div>
              </div>
              <span class="HOEnZb"><font color="#888888">-- <br>
                </font></span>
              <div class="m_6004932123691587237gmail_signature"
                data-smartmail="gmail_signature">
                <div dir="ltr">
                  <div>
                    <div dir="ltr"><span class="HOEnZb"><font
                          color="#888888">Martina Lessio, Ph.D.
                          <div>Frontiers of Science Lecturer in
                            Discipline</div>
                        </font></span><span class="">
                        <div>Postdoctoral Research Scientist</div>
                        <div>Department of Chemistry</div>
                        <div>Columbia University</div>
                      </span></div>
                  </div>
                </div>
              </div>
            </div>
          </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>
      <br>
      <fieldset class="mimeAttachmentHeader"></fieldset>
      <br>
      <pre wrap="">_______________________________________________
users mailing list
<a class="moz-txt-link-abbreviated" href="mailto:users@lists.quantum-espresso.org">users@lists.quantum-espresso.org</a>
<a class="moz-txt-link-freetext" href="https://lists.quantum-espresso.org/mailman/listinfo/users">https://lists.quantum-espresso.org/mailman/listinfo/users</a></pre>
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