Molecular dynamics simulations and density functional theory calculations were made of the diffusion of Cu adatom and dimer on Ag(111). Potentials generated by the embedded-atom method were used for the molecular dynamics simulations, and pseudopotentials derived from the projected-augmented-wave method were used for the density functional theory calculations. The molecular dynamics simulations (at three different temperatures: 300, 500, and 700K) show that the diffusivity has an Arrhenius behavior. The effective energy barriers obtained from the Arrhenius plots were in excellent agreement with those extracted from scanning tunnelling microscopy experiments. While the diffusion barrier for Cu monomers on Ag(111) was higher than that reported (both in experiment and theory) for Cu(111), the reverse holds for dimers [which, for Cu(111), has so far only been theoretically assessed]. In comparing the present molecular dynamics result with those for Cu islets on Cu(111), it was concluded that the higher barriers for Cu monomers on Ag(111) results from the comparatively large Ag-Ag bond length, whereas for Cu dimers on Ag(111) the diffusivity was taken over and boosted by the competition in optimization of the Cu-Cu dimer bond and the five nearest-neighbor Cu-Ag bonds. The present density functional theory calculations confirm the relatively large barriers for the Cu monomer on Ag(111) - 69 and 75meV - compared to those on Cu(111) and hint a rationale for them. In the case of the Cu dimer, the relatively long Ag-Ag bond length makes available a diffusion route whose highest relevant energy barrier was only 72 meV and which was not favorable on Cu(111). This process, together with another involving an energy barrier of 83 meV, establishes the possibility of low-barrier inter-cell diffusion by purely zigzag mechanisms.

Diffusion of the Cu Monomer and Dimer on Ag(111) - Molecular Dynamics Simulations and Density Functional Theory Calculations. S.S.Hayat, M.A.Ortigoza, M.A.Choudhry, T.S.Rahman: Physical Review B, 2010, 82[8], 085405