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## polarization

Moderators: mverstra, aromero

suman
Posts: 13
Joined: Fri Jan 24, 2020 5:25 pm

### polarization

Hi,
Does abinit calculate out of plane polarization?
Thank you

dbennett1994
Posts: 7
Joined: Sat Mar 21, 2020 10:21 am

### Re: polarization

By out of plane, do you mean for a semi-periodic system like a thin film? If so, it is not so straightforward to calculate polarizations. I would recommend looking at this tutorial. It describes two different methods of calculating polarizations in thin films: one using the electrostatic potential obtained using the macroave ultility, and the other using an approximate 'layer by layer' local polarization using the bulk Born effective charges and the atomic displacements in the thin film. While this tutorial is for siesta and not abinit, abinit also uses macroave to calculate macroscopic potentials and densities. And for the 'layer by layer' polarization, all you need is the bulk Born effective charges, and the relaxed geometry of the thin film. So you could easily follow both methods in this tutorial using your abinit calculations

suman
Posts: 13
Joined: Fri Jan 24, 2020 5:25 pm

### Re: polarization

My system is monolayer alpha In2Se3 which has predominant out of plane polarization.

Actually I calculated Polarization based on Berry phase calculation provided in abinit website in the link[ https://docs.abinit.org/topics/Berry/].

The output file pops out with no errors

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

I don't have much understanding about the result.
My understanding says

polarization (pol) along x = 0.075 C/m^2
polarization (pol) along y = 0.045 C/m^2
polarization (pol) along z= -0.00611 C/m^2

Literature says those material has predominant Out of plane polarization.
In my setup out of plane is along z axis and vacuum is along z axis too.

As pol along x involves quantum of polarization so it should be less than 0.075 and same holds for y.
My question is
1. Does pol along z which is -0.00611 involves quantum of polarization?
I believe it shouldn't as out of plane polarization involves vacuum.

Also whenever literature reports out of plane polarization are they using Berry phase method or something else.

2. Does Berry phase method only apply for in plane polarization?
I am confused so any of your help would be really appreciable.
Thank you

ebousquet
Posts: 469
Joined: Tue Apr 19, 2011 11:13 am
Location: University of Liege, Belgium

### Re: polarization

Dear Suman,
You should look at the link dbennett1994 gave you (and Stengel reference given there) regarding calculation of Polarization because once you play with hetero-structures, slabs, etc, the proper variable to look at should be D.
Additionally, computing P requires to have a zero reference and checking whether you follow the same "polarization branch", but I agree that the quantum along the z direction should be large enough. Please have a look at:
http://palata.fzu.cz/abinitschool/downl ... zation.pdf
Best wishes,
Eric

suman
Posts: 13
Joined: Fri Jan 24, 2020 5:25 pm

### Re: polarization

Thank you for the reply and I will work on that.