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<p>Hello Pascal,</p>
<p>Don't forget the polarization quantum : the jump at z=0.5 looks like coming from a quantum of polarization and can be removed (I mean by adding 1 to your numbers for z > 0.5). In principle, variation of P should remain small between points on your path.</p>
<p>Why don't you have the value for z=0 ?</p>
<p>Best wishes,</p>
<p>Daniel</p>
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<p>Le 2018-02-26 22:13, pboulet a écrit :</p>
<blockquote type="cite" style="padding-left:5px; border-left:#1010ff 2px solid; margin-left:5px; width:100%"><!-- html ignored --><!-- head ignored --><!-- meta ignored -->Dear all,
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<div>Does anyone have tried to used Jiang, Levchenko and Rappe’s method to calculate oxidation state of atoms? (Phys. Rev Letters, 108, 2012, 166403.</div>
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<div>In brief, the formula is N=V/e \Delta(<span style="text-decoration: underline;">P</span>) x <span style="text-decoration: underline;">R</span> /<span style="text-decoration: underline;">R</span>^2,</div>
<div>where N, V, e, \Delta(<span style="text-decoration: underline;">P</span>) and <span style="text-decoration: underline;">R</span> are the oxidation state, cell volume, electron charge, change in polarisation and lattice vector, respectively. \Delta(<span style="text-decoration: underline;">P</span>) x <span style="text-decoration: underline;">R</span> corresponds to the dot product.</div>
<div>The idea is just to displace an atom along a path traversing the cell in a way that the atom goes from its location to that in the next cell.</div>
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<div> I have tried with the PbTiO3 example of QE for the calculation of polarization via the Berry phase. If I am right I should obtain +2 as an oxidation state. </div>
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<div>I have displaced the Pb atom (crystal position at 0. 0. 0.) along the z axis from 0 to 1. </div>
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<div>The enclosed picture depicts N versus z for z=0..1. I used the polarization P given by QE in units of (e/Omega).bohr, since it is similar to the formula above.</div>
<div>I have just divided P by z since Delta(P) and R are collinear… and I guess V/e of the formula cancels with e/Omega… I am not sure of these assumptions, however…</div>
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<div>First the variation is -2 instead of +2. In addition the evolution is not smooth and the missing points on the curve are calculated to be negative. I have removed them but it is nonsense to me. </div>
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<div>Does anyone know what is wrong?</div>
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<div>Thank you for your suggestions,</div>
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<div>Pascal</div>
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