Adsorption of Chlorine on Cu(111): A Density-Functional Theory Study

The dissociative adsorption of chlorine on a perfect Cu(111) surface has been studied and characterized by means of extensive density functional theory calculations. A few properties of the bulk chlorides CuCl and CuCl2 are also reported, because they may be viewed as a limiting case for Cl adsorption. Calculations predict that the chemisorption energy of Cl at low coverage is about -1.9 eV and remains so up to the coverage of 1/3 ML due to a good screening of metal electrons. Upon further increase of coverage, its magnitude decreases. It is further found that the substitutional adsorption mode is unstable, except at very large coverage (3/4 ML), where the mixed on-surface + substitutional structure is the most stable. The diagram of the adsorption free energy as a function of chlorine chemical potential reveals that the on-surface (root 3 x root 3)R30 degrees adsorption phase is thermodynamically the most stable over a very broad range of Cl chemical potentials. The analysis of electronic structure points out that although the Cl adatoms are negatively charged, which results in an increase of the work function, the Cl-Cu interaction is not purely ionic but is to some extend also covalent, as witnessed by the formation of bonding and antibonding states. Results reveal that several Cl adsorption properties are almost unchanged Lip to the coverage of 1/3 ML, and at larger coverage, several new characteristics appear, such as occupation of nonoptimal surface sites, reduction of adatom net charge, and more covalent nature of the adsorbate-substrate interaction.