[Pw_forum] Berry Phase calculation - THE INFLUENCE OF THE ATOMIC MODEL

[Paolo Giannozzi]

Polarization is defined modulo a polarization quantum. Note the "(mod
0.3458)" in the output: the two numbers you mention differ by (almost
exactly) two times that factor

Paolo

On Mon, Sep 7, 2015 at 5:00 PM, Francesco Pelizza <
francesco.pelizza at strath.ac.uk> wrote:

> Hi dear Users,
>
> I am experiencing the event where the total polarization of the material I
> am studying (PVDF), do not always give the same outcome if I change the
> number of atoms, switching from the normal cell to a super cell containing
> more atoms than the minimum.
>
> Is always the same with the same atomic model, but is not if I change the
> model !!
>
> Here attached you can find the input file and output file of the two
> atomistic models. The first is made with 12 atoms, the second with 24, but
> is always PVDF in the same crystal phase, the Beta one.
>
> in the 12 atoms model I have  a result of  0.5231 C/M^2
> in the 24 atoms model I have  a result of -0.1683 C/M^2
>
>
> Actually, I am not fully sure if I get wrong with the berry phase
> calculation settings, or I am ignoring some important aspects of the
> software and or the calculation that justify this, and I have to learn how
> to interpret the results?
>
> I tested QE on my machine with pervoskites and nothing goes wrong, the
> results of the essential atomic models fully agree with literature.
>
> Can you give me a hand in understanding why this is happening?
>
> Thank you very much to anyone !!!
>
> Francesco Pelizza
>
> PhD student, Starthclyde, Glasgow, Scotland
>
>
>
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>



-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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