  Ferroelectric crystals must adopt one of the 10 polar point groups according
to the Neumann's principle. In this paper we propose that this conclusion is
based on perfect bulk crystals without taking the boundaries into account, and
we show first-principles evidence that ferroelectric polarizations may also be
formed in some non-polar point groups as the edges generally break the crystal
symmetry, which may even maintain at macroscale. They can be switchable in some
systems with weak van der Waals bondings or covalent-like ionic bondings where
long ion displacements with moderate barriers are possible. Such unconventional
ferroelectricity violates the Neumann's principle and Abrahams' conditions
respectively due to the boundaries and long ion displacements, which may
explain some unclarified phenomena reported previously as well as significantly
expand the scope of ferroelectrics.
