<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Dear all,<div class=""><br class=""></div><div class="">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><div class=""><br class=""></div><div class="">In brief, the formula is N=V/e \Delta(<u class="">P</u>) x <u class="">R</u> /<u class="">R</u>^2,</div><div class="">where N, V, e, \Delta(<u class="">P</u>) and <u class="">R</u> are the oxidation state, cell volume, electron charge, change in polarisation and lattice vector, respectively. \Delta(<u class="">P</u>) x <u class="">R</u> corresponds to the dot product.</div><div class="">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><div class=""><br class=""></div><div class=""> 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><div class=""><br class=""></div><div class="">I have displaced the Pb atom (crystal position at 0. 0. 0.) along the z axis from 0 to 1. </div><div class=""><br class=""></div><div class="">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 class="">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><div class=""><br class=""></div><div class="">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><div class=""><br class=""></div><div class="">Does anyone know what is wrong?</div><div class=""><br class=""></div><div class="">Thank you for your suggestions,</div><div class=""><br class=""></div><div class="">Pascal</div><div class=""><br class=""></div><div class=""></div></body></html>