  We study ferroelectric domain walls in barium titanate. We search for
structurally nontrivial, so-called non-Ising domain walls, where the
Polarisation is non-zero along the entire wall. Our approach enables us to find
solutions for domain walls in any orientation, and the existence and energy of
these walls depend on their particular orientation. We find that, across all
phases of the material, there are orientations where the non-Ising walls have
lower energy than Ising walls. The most interesting property of these domain
walls is their non-monotonic interaction forces, allowing them to form stable
domain-wall clusters rather than following standard behavior where domain walls
annihilate or repel each other. We found the required external electric field
to create the non-Ising configurations. Besides theoretical interest, this
unconventional property of domain walls makes them a good candidate for memory
application.
