Computer simulation of surface and adatom properties of Lennard-Jones solids: A comparison between face-centered-cubic and hexagonal-close-packed structure

摘要

We introduce a new mqlecular dynamics simulation path to easily calculate solid-vapor surface free energies. The .method is illustrated with explicit calculations of the surface free energies of a face-centered-cubic (fcc) crystal (the [110], [111], and [100] surfaces) and a, hexagonal-close-packed (hcp) crystal (the [111] surface) of Lennard-Jones atoms. We verify that, because of the reduced symmetry at.. interfaces, simulation of the surface structure and free energy requires a large cutoff distance for the range of the pair potential. To estimate when a growing crystal resolves the fcc/hcp structural ambiguity , we observe the binding free energy and dynamics of clusters of adatoms on [ 111] surfaces of fcc and hcp crystals. A structural distinction only appears when clusters become large enough that their slow translational motion allows a structural relaxation of the crystal ' s surface. From the observed distribution over cluster structures we deduce thermodynamic parameters that can be used to model the equilibrium between fcc-like clusters and hcp-like clusters on [111] surfaces and the rate of transformation between these.