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    <div class="moz-cite-prefix">On 23/07/2016 14:23, Muhammad Adnan
      Saqlain wrote:<br>
    </div>
    <blockquote
cite="mid:CAHULeACM9z+YuHU+xMSj6asn5ygO5KDMduGvYWhF30=4fwToUg@mail.gmail.com"
      type="cite">
      <div dir="ltr">Dear S<span style="font-size:12.8px">tefano</span>
        <div>thanks for your response.</div>
        <div>Can you please guide me (1) Why vc-relax is not allowed in
           Q-E 5.4.0?</div>
      </div>
    </blockquote>
    it is.<br>
    <blockquote
cite="mid:CAHULeACM9z+YuHU+xMSj6asn5ygO5KDMduGvYWhF30=4fwToUg@mail.gmail.com"
      type="cite">
      <div dir="ltr">
        <div>(2) How would the band gap be effected if I relax the cell
          without hybrid scheme and then calculate band gap with hybrid
          one?<br>
        </div>
        <div><br>
        </div>
      </div>
    </blockquote>
    it would be the band gap of a different structure. <br>
    it would depend on how different the structure would be with a
    different functional.<br>
     <br>
    stefano<br>
    <blockquote
cite="mid:CAHULeACM9z+YuHU+xMSj6asn5ygO5KDMduGvYWhF30=4fwToUg@mail.gmail.com"
      type="cite">
      <div class="gmail_extra"><br>
        <div class="gmail_quote">On Sat, Jul 23, 2016 at 1:07 PM,
          stefano de gironcoli <span dir="ltr"><<a
              moz-do-not-send="true" 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">
              <div>dear Muhammad Adnan Saqlain,<br>
                  <br>
                   gamma extrapolation is a way to deal with the ill
                defined value of the exchange integral between wfcs at k
                and k+q in the limit of q->0.<br>
                   if you use a truncated coulomb interaction that limit
                is not ill defined.<br>
                   no need to use the gamma_extrapolation option<br>
                   best,<br>
                stefano<br>
                <br>
                On 23/07/2016 10:00, Muhammad Adnan Saqlain wrote:<br>
              </div>
              <blockquote type="cite">
                <div dir="ltr">Dear Prof Clavijo
                  <div>I am extremely sorry for my misleading title of
                    the calculation. Actually, It was a cubic structure
                    consisting of Cs, Pb and I. I deliberately did not
                    put the atoms in the calculation. more over I do not
                    know why the algorithm for cell movement was not
                    copied it was however present in the input file.</div>
                  <div><br>
                  </div>
                  <div>1. If I try these two options, the </div>
                  <a moz-do-not-send="true"
                    name="m_1337774494978436259_m_4755999124063804085_exxdiv_treatment"
style="color:rgb(0,0,0);font-size:12.8px;font-family:arial,helvetica,sans-serif">
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                      rgb(181,181,0);margin-bottom:10px;table-layout:auto"
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                          <td colspan="2" align="left" valign="top">
                            <blockquote>
                              <pre style="white-space:pre-wrap">vcut_spherical : appropriate for cubic and quasi-cubic supercells
vcut_ws : appropriate for strongly anisotropic supercells, see also
          ecutvcut.</pre>
                            </blockquote>
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                  </a>
                  <div class="gmail_extra">the program says like this</div>
                  <div class="gmail_extra">
                    <div class="gmail_extra"><br>
                    </div>
                    <div class="gmail_extra">%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%</div>
                    <div class="gmail_extra">     Error in routine
                       system_checkin (1):</div>
                    <div class="gmail_extra">      x_gamma_extrapolation
                      cannot be used with vcut</div>
                    <div class="gmail_extra"> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%</div>
                    <div><br>
                    </div>
                  </div>
                  <div class="gmail_extra">I have no idea how to fix it.
                    Can you suggest one??</div>
                  <div class="gmail_extra"><br>
                  </div>
                  <div class="gmail_extra">2. I have now used Q-E 5.4.0,
                    but this version does not allow vc-relax option with
                    hybrid one. why is it so? How would the band gap be
                    effected if I relax the cell without hybrid scheme
                    and then calculate band gap with hybrid one?</div>
                  <div class="gmail_extra"><br>
                  </div>
                  <div class="gmail_extra">3. About the ecutoff, I
                    deliberately used small one as these are just
                    calculations not the real one.</div>
                  <div class="gmail_extra">4. I have cubic system, may I
                    try q-grid like 1*2*3 or it has to be symmetric one?</div>
                  <div class="gmail_extra"> 5. Can you suggest more
                    about hybrid calculations?</div>
                  <div class="gmail_extra"><br>
                  </div>
                  <div class="gmail_extra"><br>
                    <div class="gmail_quote">On Fri, Jul 22, 2016 at
                      10:09 PM, Josue Itsman Clavijo Penagos <span
                        dir="ltr"><<a moz-do-not-send="true"
                          href="mailto:jiclavijop@unal.edu.co"
                          target="_blank">jiclavijop@unal.edu.co</a>></span>
                      wrote:<br>
                      <blockquote class="gmail_quote" style="margin:0px
                        0px 0px
0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">
                        <div dir="ltr">Dear, Muhammad Adnan Saqlain,
                          remember the user documentation for <b
                            style="font-size:13px">exxdiv_treatment</b>: <a
                            moz-do-not-send="true"
                            name="m_1337774494978436259_m_4755999124063804085_exxdiv_treatment"
style="color:rgb(0,0,0);font-family:arial,helvetica,sans-serif">
                            <table style="border:2px solid
                              rgb(181,181,0);margin-bottom:10px;table-layout:auto"
                              width="100%">
                              <tbody>
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                                  <td colspan="2" align="left"
                                    valign="top">
                                    <blockquote>
                                      <pre>Specific for EXX. It selects the kind of approach to be used
for treating the Coulomb potential divergencies at small q vectors.

gygi-baldereschi : appropriate for cubic and <b>quasi-cubic supercells</b>
vcut_spherical : appropriate for cubic and quasi-cubic supercells
vcut_ws : appropriate for strongly anisotropic supercells, see also
          ecutvcut.
none : sets Coulomb potential at G,q=0 to 0.0 (required for GAU-PBE)</pre>
                                    </blockquote>
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                          </a><b>Besides that, </b>I<b> </b>have some
                          observations and suggestions for you based in
                          the input file you send, so you can realize
                          why does QE is failing when trying to simulate
                          your system:
                          <div><br>
                          </div>
                          <div>1 - Check if you really need to apply
                            smearing, since this technique is intended
                            to be useful for metallic systems, and
                            Anatase is cleary not a metallic system, in
                            fact, is more a Wide-gap or Insulator -type
                            system.<br>
                            <div><br>
                            </div>
                            <div>2 - You do want to perform a vc-relax
                              calculation, but nothing are specified in
                              the cards &IONS and &CELL. There
                              is not cell relaxing algorithm specified
                              (BFGS? MD?)</div>
                          </div>
                          <div><br>
                          </div>
                          <div>3 - The card &ATOMIC_POSITIONS shows
                            nothing: No atoms, no cell to relax.</div>
                          <div><br>
                          </div>
                          <div>4 - In the card &SYSTEM , <b>ecutwfc
                              = 40.</b> This, in my humble opinion, a
                            very poor cutoff for a serious calculation.
                            Do a ecutwfc convergence test before attempt
                            your system.</div>
                          <div><br>
                          </div>
                          <div>5 - Please take in account that a hybrid
                            calculation is VERY expensive in terms of
                            computational demand, so if you set up a
                            vc-relax calculation using hybrid PPS you
                            must test if <b style="font-size:13px">nqx1
                              = 1, 2 or 3 really makes a difference.</b></div>
                          <div><b style="font-size:13px"><br>
                            </b></div>
                          <div><b>6 - For some systems, input_dft=HSE is
                              faster than </b><b>input_dft = "PBE0".
                              Check if that could be your case.</b></div>
                          <div><b><br>
                            </b></div>
                          <div>By the way, are you sure Anatase has a
                            cubic crystal structure? Does XCrysden show
                            the correct structure for your input?</div>
                          <div><br>
                          </div>
                          <div><b>Best regards, </b></div>
                          <div><b><br>
                            </b></div>
                          <div class="gmail_extra"><br>
                            <div class="gmail_quote">Josué Clavijo, PhD.</div>
                            <div class="gmail_quote">Assistant Professor</div>
                            <div class="gmail_quote">Universidad
                              Nacional de Colombia</div>
                            <div class="gmail_quote">Departamento de
                              Química</div>
                          </div>
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                        <div><br>
                        </div>
                        -- <br>
                        <div data-smartmail="gmail_signature">
                          <div dir="ltr">Best Regards
                            <div>Muhammad Adnan Saqlain
                              <div><br>
                              </div>
                            </div>
                          </div>
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        -- <br>
        <div class="gmail_signature" data-smartmail="gmail_signature">
          <div dir="ltr">Best Regards
            <div>Muhammad Adnan Saqlain
              <div><br>
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