Hello Pascal,
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. Why don't you have the value for z=0 ? Best wishes, Daniel Le 2018-02-26 22:13, pboulet a écrit : > Dear all, > > Does anyone have tried to used Jiang, Levchenko and Rappe's method to calculate oxidation state of atoms? (Phys. Rev Letters, 108, 2012, 166403. > > In brief, the formula is N=V/e Delta(P) x R /R^2, > where N, V, e, Delta(P) and R are the oxidation state, cell volume, electron charge, change in polarisation and lattice vector, respectively. Delta(P) x R corresponds to the dot product. > 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. > > 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. > > I have displaced the Pb atom (crystal position at 0. 0. 0.) along the z axis from 0 to 1. > > 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. > 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… > > 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. > > Does anyone know what is wrong? > > Thank you for your suggestions, > > Pascal > > Pascal Boulet > -- > _Professor in computational chemistry - DEPARTMENT OF CHEMISTRY_ > > Director of the Madirel laboratory > Aix-Marseille University - Avenue Escadrille Normandie Niemen - F-13013 Marseille - FRANCE > Tél: +33(0)4 13 55 18 10 et +33(0)4 13 55 18 19 - Fax : +33(0)4 13 55 18 50 > Email : [email protected] > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum [1] Links: ------ [1] http://pwscf.org/mailman/listinfo/pw_forum
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