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    <p><font face="Helvetica, Arial, sans-serif">Hi,</font></p>
    <p><font face="Helvetica, Arial, sans-serif">GGA is certainly
        inadequate to sytudy this system. My recommendation would be to
        carry out a hybrid functional calculation, e.g. with HSE. This
        cell has not too may atoms, it should be feasible. Use at least
        a 4x4x4 Brillouin zone sampling. Displacing Fe from the symmetry
        position is of course necessary, then the structure should be
        relaxed. And a spin-polarized calculation will be necessary as
        well. I find likely that the system will have in the end a low
        spin configuration, with all Fe(3d) electrons filling the t(2g)
        manifold which would be well separated from the e(g) manifold,
        therefore having a clear nonmetallic behaviour.</font></p>
    <p>Good luck,</p>
    <p>JC Conesa<br>
    </p>
    <br>
    <div class="moz-cite-prefix">El 04/03/2018 a las 9:51, Pietro
      Delugas escribió:<br>
    </div>
    <blockquote type="cite"
      cite="mid:13055429-a122-4ec6-9d66-1aeeb3b1a3d6@email.android.com">
      <div dir="auto">
        <div>If the band is flat or almost flat maybe one could try to
          use LDA+U, ( or some hybrid functional with exact exchange if
          the cell size is  feasible ) displace Fe a little if it is in
          a  too symmetric position, relax and see if it is possible to
          split Fe impurity levels. If so one can  compute Fe Born
          Charges by finite differences. </div>
        <div dir="auto"><br>
        </div>
        <div dir="auto">
          <div class="gmail_extra" dir="auto"><br>
            <div class="gmail_quote">Il 04 mar 2018 9:27 AM, Paolo
              Giannozzi <a class="moz-txt-link-rfc2396E" href="mailto:p.giannozzi@gmail.com"><p.giannozzi@gmail.com></a> ha scritto:<br
                type="attribution">
              <blockquote class="quote" style="margin:0 0 0
                .8ex;border-left:1px #ccc solid;padding-left:1ex">
                <div dir="ltr">
                  <div>The problem is that the true system is not
                    metallic, but in a band picture it is, even for a
                    supercell of 1m side. Maybe one might compute
                    phonons as for a metal, then use dielectirc constant
                    and effective charges of the insulating host
                    crystal. Not sure what one can use for the effective
                    charges of Fe, though.<br>
                    <br>
                  </div>
                  Paolo<br>
                </div>
                <div><br>
                  <div class="elided-text">On Sun, Mar 4, 2018 at 8:39
                    AM, Pietro Delugas <span dir="ltr"><<a
                        href="mailto:pdelugas@sissa.it"
                        moz-do-not-send="true">pdelugas@sissa.it</a>></span>
                    wrote:<br>
                    <blockquote style="margin:0 0 0
                      0.8ex;border-left:1px #ccc solid;padding-left:1ex">
                      <div dir="auto">
                        <div>Hello Chris</div>
                        <div dir="auto"><br>
                        </div>
                        <div dir="auto">If the system is metallic, no
                          matter how bad a conductor it can be, in a
                          finite time it will be able to screen any
                          constant electric field. This  is as to say
                          that the static dielectric constant is
                          infinite. </div>
                        <div dir="auto"><br>
                        </div>
                        <div dir="auto">Regards Pietro
                          <div>
                            <div><br>
                              <div dir="auto"><br>
                                <div class="elided-text">Il 04 mar 2018
                                  8:03 AM, Christoph Wolf
                                  <a class="moz-txt-link-rfc2396E" href="mailto:wolf.christoph@qns.science"><wolf.christoph@qns.science></a> ha
                                  scritto:<br>
                                  <blockquote style="margin:0 0 0
                                    0.8ex;border-left:1px #ccc
                                    solid;padding-left:1ex">
                                    <div dir="ltr">Dear all,
                                      <div><br>
                                      </div>
                                      <div>I have a fairly general
                                        question and I hope I can pick
                                        someone's brain:</div>
                                      <div><br>
                                      </div>
                                      <div>If an insulator or
                                        semiconductor is doped with a
                                        metal narrow bands determined by
                                        the crystal field emerge and
                                        often the fermi level lies
                                        within one of the bands, i.e.
                                        the "bands cut the fermi level",
                                        which is often called a
                                        characteristic of a conductor
                                        but in the bigger picture no
                                        electrons would be able to cross
                                        from the VB to the CB, i.e. the
                                        host system is an insulator.</div>
                                      <div><br>
                                      </div>
                                      <div>When attempting to calculate
                                        the phonons of a Mg7O8Fe
                                        supercell the  dieletric
                                        constant (in the case of pure
                                        MgO eps~3.1) cannot be computed</div>
                                      <div><br>
                                      </div>
                                      <div>
                                        <div>     Electric Fields
                                          Calculation</div>
                                        <div>     ik   1 ibnd   0
                                          linter: root not converged 
                                          2.635E-07</div>
                                      </div>
                                      <div>....</div>
                                      <div>..</div>
                                      <div><br>
                                      </div>
                                      <div>
                                        <div>     End of electric fields
                                          calculation</div>
                                        <div><br>
                                        </div>
                                        <div>          Dielectric
                                          constant in cartesian axis </div>
                                        <div><br>
                                        </div>
                                        <div>         
                                          (******************     
                                           0.000244141      -0.001708984
                                          )</div>
                                        <div>          (     
                                          -0.000244141******************<wbr> 
                                               0.000244141 )</div>
                                        <div>          (     
                                          -0.000732422     
                                           0.000732422******************
                                          )</div>
                                        <div><br>
                                        </div>
                                        <div>And I am wondering if that
                                          system should be treated as a
                                          metal instead (epsil    =
                                          .false.,) during the phonon
                                          run?</div>
                                        <div><br>
                                        </div>
                                        <div>
                                          <div>--</div>
                                          <div>&inputph</div>
                                          <div>  prefix   = 'MgO',</div>
                                          <div>  epsil    = .true.,</div>
                                          <div>  alpha_mix(1) =0.4</div>
                                          <div>  alpha_mix(2) =0.4</div>
                                          <div>  fildyn   = 'MgO.dyn',</div>
                                          <div>  ldisp    = .true.</div>
                                          <div>  fildvscf = 'dvscf'</div>
                                          <div>  amass(1) = 24.30500</div>
                                          <div>  amass(2) = 15.99900</div>
                                          <div>  amass(3) = 55.84500</div>
                                          <div>  outdir='./',</div>
                                          <div>  nq1=6,</div>
                                          <div>  nq2=6,</div>
                                          <div>  nq3=6,</div>
                                          <div>  tr2_ph   =  1.0d-12,</div>
                                          <div> /</div>
                                        </div>
                                        <div><br>
                                        </div>
                                        <div>Any hint is welcome!</div>
                                        <div><br>
                                        </div>
                                        <div>Thanks in advance for your
                                          help and a nice Sunday
                                          everyone!</div>
                                        <div><br>
                                        </div>
                                        <div>Chris </div>
                                        -- <br>
                                        <div>
                                          <div dir="ltr">Postdoctoral
                                            Researcher<br>
                                            Center for Quantum
                                            Nanoscience, Institute for
                                            Basic Science<br>
                                            Ewha Womans University,
                                            Seoul, South Korea</div>
                                        </div>
                                      </div>
                                    </div>
                                  </blockquote>
                                </div>
                                <br>
                              </div>
                            </div>
                          </div>
                        </div>
                      </div>
                      <br>
                      ______________________________<wbr>_________________<br>
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                    </blockquote>
                  </div>
                  <br>
                  <br clear="all">
                  <br>
                  -- <br>
                  <div data-smartmail="gmail_signature">
                    <div dir="ltr">
                      <div>
                        <div dir="ltr">
                          <div>Paolo Giannozzi, Dip. Scienze Matematiche
                            Informatiche e Fisiche,<br>
                            Univ. Udine, via delle Scienze 208, 33100
                            Udine, Italy<br>
                            Phone +39-0432-558216, fax +39-0432-558222<br>
                            <br>
                          </div>
                        </div>
                      </div>
                    </div>
                  </div>
                </div>
              </blockquote>
            </div>
            <br>
          </div>
        </div>
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      <br>
      <pre wrap="">_______________________________________________
users mailing list
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    </blockquote>
    <br>
    <pre class="moz-signature" cols="72">-- 
José C. Conesa
Instituto de Catálisis y Petroleoquímica, CSIC
Marie Curie 2, Cantoblanco
28049 Madrid, Spain
Tel. (+34)915854766</pre>
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