polarization in In2Se3

[suman]

Hi abinit users,

I am trying to calculate polarization of monolayer In2Se3.
It has predominant out of plane polarization, my vacuum is along z axis and z is out of plane in my setup.
The output file shows that polarization along x and y is greater than along z but it shouldn't be and I don't know how.

Polarization in cartesian coordinates (C/m^2):
(the sum of the electronic and ionic Berry phase has been folded into [-1, 1])
Electronic berry phase: -0.363359383E-04 -0.209785676E-04 0.409497792E+00
Ionic: 0.755329491E-01 0.436089685E-01 -0.415614991E+00
Total: 0.754966131E-01 0.435879899E-01 -0.611719867E-02
Could you please tell me if something is incorrect in input file?
I have attached input and output file.
Any help would be highly appreciable.
Thank you

[ebousquet]

Dear Suman,
Polarization is not a direct observable and has the problem of lattice quantum, etc. This is the problem you get along x and y (quantum of polarization, not real polarization).
You have to get a zero reference structure and see how the polarization evolves with the distortion up to the ground state (all at fixed cell parameter, the ground state one) to identify the quantum of P.
Please have a look on the following lecture and read carefully the references given for the Berry phase theory of Polarization (Spaldin and Resta are meant to beginners):
http://palata.fzu.cz/abinitschool/downl ... zation.pdf
Best wishes,
Eric

[suman]

Thank you for the reply.
I will go through the link.