  We report an unexpected mechanism by which an epitaxial interface can form
between materials having strongly mismatched lattice constants. A simple model
is proposed in which one material tilts out of the interface plane to create a
coincidence-site lattice that balances two competing geometrical criteria---low
residual strain and short coincidence-lattice period. We apply this model,
along with complementary first-principles total-energy calculations, to the
interface formed by molecular-beam epitaxy of cubic Fe on hexagonal GaN and
find excellent agreement between theory and experiment.
