Hi, In the case of dielectric in electric field E0, we have E1 = E0 outside crystal and E2 = E0 - P inside, so that D1 = E1 = D2 = E2 + P. That's obvious. Now, if dielectric is ferroelectric and no external field, we have only bounded surface charges. It seems for me that E1 = 0 outside crystal and E2 = - P inside. So we have D1 = 0 outside and D2 = E2 + P = 0. But I've read (link ), that polarization close to the free surface and perpendicular to it must vanish in order to fulfill boundary condition from Maxwell equations that D1 - D2 = Qfree. Since there are no free charges, we have D1 = D2. But if we have D1 = 0 and D2 = 0, I don't see any restriction for P...? Then, if we have a metal on a ferroelectric surface (the same reference), rather than vanishing of polarization, we have free charges induced on the dielectric-metal boundary to fulfill this boundary condition. Thus... I don't know! It looks very strange for me. How to understand it?