<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 <p.giannozzi@gmail.com> 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">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 <wolf.christoph@qns.science> 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<blockquote style="font-size:12.8px"><div dir="ltr"><div><div dir="ltr"></div></div></div></blockquote></div></div>
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