Density-functional theory calculations of the adsorption of Cl at perfect and defective Ag(111) surfaces

Density functional theory calculations of adsorption of chlorine at the perfect and defective silver (111) surface have shown that the energies of adsorption of chlorine atoms show little variation (less than 30 kJ mol(-1)) between the different sites, from -136 kJ mol(-1) next to a silver adatom, through -159 kJ mol(-1) at the perfect surface to -166 kJ mol(-1) next to a silver vacancy at the surface. Molecular chlorine adsorbs in a series of energetically similar overlayers, which are in good agreement with experimentally found structures. The lowest energy configuration is a planar hexagonal honeycomb structure of chlorine atoms adsorbed in fcc and hcp hollow sites on the silver surface. An energetically similar structure is geometrically nonplanar, but has a planar electronic structure. Although the chlorine molecules are virtually dissociated (Cl-Cl distance=3.40 Angstrom), significant electron density is distributed along the Cl-Cl axes, leading to a network of electronic interactions between the adsorbed chlorine atoms. The adsorption energy for Cl-2 is calculated at -231 kJ mol(-1), in good agreement with experiment. Calculated Ag-Cl bond lengths of 2.69, 2.47, and 2.33 Angstrom agree with several experimental studies and show that the different bond lengths found experimentally are not anomalous, but due to the formation of geometrically different but energetically almost identical chlorine overlayer structures.