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Computational approach to equilibrium relaxation in central force systems

1971; Elsevier BV; Volume: 26; Issue: 1 Linguagem: Inglês

10.1016/0039-6028(71)90121-x

1879-2758

Paul A. Tick, August F. Witt,

Surface and Thin Film Phenomena

The equilibrium configurations of low index surfaces in materials subject to central force laws and the behavior of adatoms on such surfaces were investigated using pairwise interaction theory. A direct search optimization code utilizing trial solutions with both a one-variable-at-a-time search and a vector search to scan the variables for energy optimization was applied. It was found that the interplanar spacings adjacent to a planar free surface are larger than equivalent bulk spacings and that the degree of interplanar expansion diminishes rapidly with increasing depth below the surface. The magnitude of surface expansion depends strongly on the characteristics of the potential chosen to represent the crystal forces. Surfaces which terminate with a monatomic step show non-linear structures at the step edge. Adsorption energies for adatoms on such surfaces are large on (111) surfaces and smaller on (110) and (100) surfaces. They decrease with decreasing adatom mismatch and increase with less convergent binding potentials. The activation energy for adatom surface diffusion was found to be largest on the (110) surface and smaller on the (100) and (111) surfaces; it decreases with increasing adatom mismatch and increases with more convergent binding potentials. The clustering characteristics of adatoms on (100) surfaces were investigated and applied to the system silver on nickel. The results show that both (111) and (100) oriented silver films could grow simultaneously on (100) nickel surfaces. No special attempt is made to compare the computed results with other published data. The primary purpose is to indicate a novel computational approach to surface investigations.