First-Principles Study of Chlorine Adsorption on Clean Al(111)

A density functional theory model is used to investigate the structural, thermodynamic, and electronic properties of chlorine atoms adsorbed on the Al(111) surface within a supercell approach for chlorine coverages of 1/4, 1/3, 1/2, 3/4, and 1 ML. The largest bond length is observed for an atop, hcp, and fcc mixed structure at 3/4 ML coverage. Analysis of the adsorption free energy reveals that the chlorine coverage of 3/4 ML is the most thermodynamically stable over the widest range of chlorine chemical potential and that the coverage of 1 ML is thermodynamically unstable. The electronic charge density distributions, the change in the work function induced by adsorption, and the corresponding electrostatic dipole moment are also calculated. Atop-site adsorption is shown to induce charge transfer and the formation of a dipole structure for low coverage, and the charge transfer decreases with increasing coverage. Surface bonding is investigated using the projected density of states, and aluminum and chlorine 3p-orbitals are shown to be important in Al-Cl bond formation.