The results of molecular dynamics simulations and density functional theory calculations of the diffusion of Cu adatoms and dimers on Ag(111) were presented (table 5). Potentials generated by the embedded-atom method were used for the molecular dynamics simulations, and pseudopotentials derived from the projected-augmented-wave method for the density functional theory calculations. The molecular dynamics simulations (at 300, 500 and 700K) showed that the diffusivity exhibited 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 held for dimers which, for Cu(111), had previously been only theoretically assessed. Upon comparing the molecular dynamics result with those for Cu islets on Cu(111), it was concluded that the higher barriers for Cu monomers on Ag(111) resulted 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 density functional theory calculations confirmed the relatively large barriers for the Cu monomer on Ag(111)-69 and 75meV, compared to those on Cu(111). In the case of the Cu dimer, the relatively long Ag-Ag bond length made available a diffusion route whose highest relevant energy barrier was only 72meV and which was not favorable on Cu(111). This process, together with another involving an energy barrier of 83meV, established the possibility of low-barrier inter-cell diffusion via a purely zig-zag mechanism.

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

Table 5

Surface diffusivity of Cu on Ag (111)