  We present two approaches for coarse-graining interplanar potentials and
determining the corresponding macroscopic cohesive laws based on energy
relaxation and the renormalization group. We analyze the cohesive behavior of a
large---but finite---number of interatomic planes and find that the macroscopic
cohesive law adopts a universal asymptotic form. The universal form of the
macroscopic cohesive law is an attractive fixed point of a suitably-defined
renormalization-group transformation.
