| 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 |
polar_scf.pdf
Description: Adobe PDF document
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
