Structural and dynamical behavior of noble-gas surfaces

Molecular-dynamics calculations have been performed for noble-gas (krypton) surfaces. As pair potential between the particles, we used the potential of Barker et al. This potential is consistent with a wide range of experimental data and should be more realistic than the more familiar Lennard-Jones (6-12) potential. The calculations have been performed for temperatures of 7, 70, and 102 K. We used the following model: The krypton atoms are arranged as a slab-shaped fcc crystal, the two free surfaces being (100) planes. The slab consists of 11 layers of 50 atoms, i.e., the total number of particles used in the calculations was 550. The structure of the layers has been studied by means of the single-particle distribution function and the pair correlation function. Whereas the results for the innermost layer of the model agree well with the corresponding data of the bulk, there are relatively large effects for the outermost layer. This is also the case for the mean-square displacements 〈$u^2$〉, which is much larger in the outermost layer than in the bulk of the crystal. For T=102 K, we observe the effect of surface premelting: The outermost layer is disordered and the particles perform a diffusive motion parallel to the surface and the diffusion coefficient D is comparable to that in liquids. The effect of premelting in our system is obviously much more pronounced than in the case of Lennard-Jones systems.