  A phase eld approach is developed to model wetting and heterogeneous crystal
nucleation of an undercooled pure liquid in contact with a sharp wall. We
discuss various choices for the boundary condition at the wall and determine
the properties of critical nuclei, including their free energy of formation and
the contact angle as a function of undercooling. We nd for particular choices
of boundary conditions, we may realize either an analog of the classical
spherical cap model or decidedly non-classical behavior, where the contact
angle decreases from its value taken at the melting point towards complete
wetting at a critical undercooling.
