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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>
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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>
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</div>
</blockquote>
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<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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