  Using a thermodynamic integration scheme, we compute the free energy cost per
unit area, $\gamma$, of forming an interface between a crystal and a frozen
structured wall, formed by particles frozen into the same equilibrium structure
as the crystal. Even though the structure and potential energy of the
crystalline phase in the vicinity of the wall is same as in the bulk, $\gamma$
has a non-zero value and increases with increasing density of the crystal and
the wall. Investigating the effect of several interaction potentials between
the particles, we observe a positive $\gamma$ at all crystalline densities if
the potential is purely repulsive. For models with attractive interactions,
such as the Lennard-Jones potential, a negative value for $\gamma$ is obtained
at low densities.
