Sb-induced surface stacking faults at Ag(111) and Cu(111) surfaces: density-functional theory results

Using the CASTEP computer code we have conducted structural optimization calculation in the generalized-gradient approximation for the Ag(lll)(root 3 x root 3)R30 degrees-Sb and Cu(lll)(root 3 x root 3)R30 degrees-Sb surface phases with a view to exploring the findings of several recent experimental studies which indicate that the outermost surface alloy layer in these surfaces contains substrate and Sb atoms in the hcp hollow sites, leading to a stacking fault at the alloy-substrate interface. The results confirm that these structures do have lower total energy than the unfaulted geometries. In Ag(lll) the stacking fault energy for a clean surface layer is especially low, and becomes negative in the presence of the partial Sb substitution. The relative energies of alternative Sb surface structures on Ag(lll) are consistent with those of previous theoretical calculations, while the detailed geometry of the two optimal structures agrees well with experimental results.