Nature of Cl bonding on the Au(111) surface: evidence of a mainly covalent interaction.

We report theoretical evidence from first-principles density functional theory (DFT) calculations that the bonding between Cl and the Au(111) surface is primarily covalent in character, which is in contrast to the generally held view that the bonding of halogens to metal surfaces is ionic. We observe the transfer of charge density into the region between interacting Au and Cl atoms, which would not be expected in the case of Cl- anion formation (symmetric charge accumulation on Cl). Importantly, we also find a clear directionality of dz2 orbitals of the Au atoms pointing to the adsorbed Cl and the mixing of electronic states between the gold surface and the adsorbed chlorine.