[Pw_forum] calculating atoms oxidation states

[pboulet]

Hello Daniel,

Thanks for your answer. I have the value for z=0:
P =   0.0000049  (mod  14.7398000)  (e/Omega).bohr

Pascal

> Le 27 févr. 2018 à 07:09, Daniel Stoeffler <daniel.stoeffler at ipcms.unistra.fr> a écrit :
> 
> 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
>>  
>>  
>> 
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>> 
>> 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 : pascal.boulet at univ-amu.fr <mailto:pascal.boulet at univ-amu.fr>
>>  
>>  
>> 
>> 
>> 
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