Hello,
I'm performing calculations on the adsorption of OH on downward-polarized Tetragonal(P4MM) BiFeO3,

and I want to calculate whether the adsorption of OH causes ferroelectric polarization switch.

Below are my steps.
1.optimize unitcell of Tetragonal BFO
2.cleave the (001) surface
3.build a 20 Å vacuum layer
4.optimize slab
5.OH on BFO
6.optimize BFO-OH

I want to ask：
How to determine if the polarization direction has switched or not?

Thanks.