  Using Molecular Dynamics (MD) and Monte Carlo (MC) simulations interfacial
properties of crystal-fluid interfaces are investigated for the hard sphere
system and the one-component metallic system Ni (the latter modeled by a
potential of the embedded atom type). Different local order parameters are
considered to obtain order parameter profiles for systems where the crystal
phase is in coexistence with the fluid phase, separated by interfaces with
(100) orientation of the crystal. From these profiles, the mean-squared
interfacial width w^2 is extracted as a function of system size. We rationalize
the prediction of capillary wave theory that w^2 diverges logarithmically with
the lateral size of the system. We show that one can estimate the interfacial
stiffness from the interfacial broadening, obtaining 0.5 k_B T/sigma^2 for hard
spheres and 0.18 J/m^2 for Ni.
