Ab initio calculations for bromine adlayers on the Ag(100) and Au(100) surfaces: The $c(2\mathrm{}\times 2)$ structure

Ab initio total-energy density-functional methods with supercell models have been employed to calculate the $c(2\mathrm{}\times 2)$ structure of the Br-adsorbed Ag(100) and Au(100) surfaces. The atomic geometries of the surfaces and the preferred bonding sites of bromine have been determined. The bonding character of bromine with the substrates has also been studied by analyzing the electronic density of states and the charge transfer. The calculations show that while the fourfold hollow-site configuration is more stable than the twofold bridge-site topology on the Ag(100) surface, bromine prefers the bridge site on the Au(100) surface. The onefold on-top configuration is the least stable configuration on both surfaces. It is also observed that the second layer of the Ag substrate undergoes a small buckling as a consequence of the adsorption of Br. Our results provide a theoretical explanation for the experimental observations that the adsorption of bromine on the Ag(100) and Au(100) surfaces results in different bonding configurations.