problem about berryphase term in calculation of ferroelectric polarization

[JuntingZhang]

When I used the berry phase method combined with non-collinear or spin-orbit coupling to calculate the ferroelectric polarization of multiferroics (i.e.,the polarization is induced by special magnetic orders which destroy the inversion symmetry), I found the berryphase terms "e<r>_bp" are nonzero along the three directions of cartesian coordinate.
While, actually, the polarization only presents in one direction.
For example, the real polarization is along the c axis in a material with R-3 symmetry, while the calculated berryphase terms along G1 and G2 (in ab plane) are
G1:
e<r>_ev=( 0.00000 0.00000 0.00031 ) e*Angst
e<r>_bp=( 0.06706 -0.03871 0.00000 ) e*Angst
G2:
e<r>_ev=( 0.00000 0.00000 0.00031 ) e*Angst
e<r>_bp=( 0.00000 -0.18442 0.00000 ) e*Angst

How should I understand the berryphase terms present in the ab plane?
In my opinion, the electron terms "e<r>_ev" can rightly reflect the polar direction except the minor values.
While, sometimes the electron term e<r>_ev equals zero and e<r>_ev has nonzero value. Does this means the polarization present?
Another question: the spin-orbit coupling should be switched on in the previous scf calculations or the succedent nscf process ( switch on berryphase ) ?

Thanks,
Junting Zhang

<span class='smallblacktext'>[ Edited ]</span>

[support_vasp]

Hi,

We're sorry that we didn’t answer your question. This does not live up to the quality of support that we aim to provide. The team has since expanded. If we can still help with your problem, please ask again in a new post, linking to this one, and we will answer as quickly as possible.

Best wishes,

VASP