Interfaces play a key role in low dimensional materials like graphene or its
boron nitrogen analog, white graphene. The edge energy of h-BN has not been
reported as its lower symmetry makes it difficult to separate the opposite
B-rich and N-rich zigzag sides. We report unambiguous energy values for
arbitrary edges of BN, including the dependence on the elemental chemical
potentials of B and N species. A useful manifestation of the additional Gibbs
degree of freedom in the binary system, this dependence offers a way to control
the morphology of pure BN or its carbon inclusions, and to engineer their
electronic and magnetic properties