Sala Seminari (Dip. Matematica).
In this talk I will introduce a free energy, first studied by Ratz and Voigt, defined as the integration over the reduced boundary of a crystal E of a suitable psi(u(x)) where psi is a convex function and u denotes the adatom density (the density of atoms not attached to the crystal and free to move on the surface). This energy leads the surface diffusion evolution in absence of the elastic stress and for small adatom densities. We treat the variational point of view, by analyzing the semicontinuity issues and the relaxad functional.