[Pw_forum] calculating atoms oxidation states

Daniel Stoeffler daniel.stoeffler at ipcms.unistra.fr
Tue Feb 27 07:09:29 CET 2018


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. 

don't you have the value for z=0 ? 

Best wishes, 


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 Boulet 
> -- 
> _Professor in computational
> Director of the Madirel
> 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 :
pascal.boulet at univ-amu.fr 
> Pw_forum mailing
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