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Dear Laurence,
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<div>it could be related to sensitivity of Born charges to the orbital hybridization since a polarization change associated with a small displacement of an atom also captures a charge transfer resulted from this displacement (<span style="caret-color: rgb(34, 34, 34); color: rgb(34, 34, 34); font-family: "Helvetica Neue", Helvetica, Roboto, Arial, sans-serif; font-size: 14px; -webkit-text-size-adjust: 100%; background-color: rgb(255, 255, 255);">https://doi.org/10.1103/PhysRevB.58.6224</span> sec.
IIIB). The charge transfer contribution is very large in perovskites with the exception of O_perpendicular. Perhaps the dielectric constant involved in evaluation of the Callen charge (eq. 9 in that paper) reduces sensitivity of the charge transfer term to
the choice of functional? It would make sense to have a large charge transfer for a system with larger polarizability.</div>
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<div>Best regards </div>
<div>Oleg</div>
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<div dir="ltr"><span style="background-color: rgba(255, 255, 255, 0);">--<br>
Oleg Rubel (PhD, PEng)<br>
Department of Materials Science and Engineering<br>
McMaster University<br>
JHE 359, <a href="x-apple-data-detectors://0/1" dir="ltr" x-apple-data-detectors="true" x-apple-data-detectors-type="address" x-apple-data-detectors-result="0/1" style="-webkit-text-decoration-color: rgba(0, 0, 0, 0.258824);">1280 Main Street West, Hamilton,
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<blockquote type="cite">On Apr 2, 2021, at 15:13, Laurence Marks <laurence.marks@gmail.com> wrote:<br>
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<div class="gmail_default" style="font-family:verdana,sans-serif;color:#000000">One of my students recently calculated the Callen & Born charges for SrTiO3, finding that the Callen charge was almost independent of functional (LDA, PBE, PBEsol, PBEsol+onsite)
whereas the Born charge was. For reference, the Bader charges are different.</div>
<div class="gmail_default" style="font-family:verdana,sans-serif;color:#000000"><br>
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<div class="gmail_default" style="font-family:verdana,sans-serif;color:#000000">I am perplexed by the invariance of the Callen charge -- any explanations?</div>
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-- <br>
<div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature">
<div dir="ltr">Professor Laurence Marks<br>
Department of Materials Science and Engineering<br>
Northwestern University<br>
<a href="http://www.numis.northwestern.edu/" target="_blank">www.numis.northwestern.edu</a>
<div>"Research is to see what everybody else has seen, and to think what nobody else has thought" Albert <span style="font-family:Arial,Helvetica,sans-serif;font-size:12.8px">Szent-</span><span style="font-family:Arial,Helvetica,sans-serif;font-size:small;color:rgb(34,34,34)">Györgyi</span></div>
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