Dear admin,
I found that for 2d FE material, the dipole moment along z direction (vacuum direction) obtained by charge integration and berry phase difference w.r.t to the centro-symmetric phase are different. I've attached the tested result here.
In principle these two value should agree with each other, but in my test, p_berry always has larger magnitude than p_charge_integrate, with p_berry ~ 1.5 p_charge_integrate for FE phase. And the difference gets larger with larger structure distortion.
My test is inspired from this post forum/viewtopic.php?p=21643#p21643. They tested on water molecules and obtain reasonable agreement. And the admin there said "polarization perpendicular to the monolayer should be computed with LDIPOL = T". But I'm still don't fully understand why and is still confused.
Best wishes
