Atomic oxygen adsorption and incipient oxidation of the Pb(111) surface: A density-functional theory study

Abstract

We study the atomic oxygen adsorption on Pb(111) surface by using density-functional theory within the generalized gradient approximation and a supercell approach. The atomic and energetic properties of purely on-surface and subsurface oxygen structures at the Pb(111) surface are systematically investigated for a wide range of coverage and adsorption sites. The fcc and tetra-II sites (see the text for definition) are found to be energetically preferred for the on-surface and subsurface adsorption, respectively, in the whole range of coverage considered. The on-surface and subsurface oxygen binding energies monotonically increase with the coverage, and the latter is always higher than the former, thus indicating a tendency to the formation of oxygen islands (clusters) and the higher stability of subsurface adsorption. The on-surface and subsurface diffusion-path energetics of atomic oxygen, as well as the activation barriers for oxygen penetration from the on-surface to the subsurface sites, are presented at low and high coverage. The other properties of the O/Pb(111) system, including the charge distribution, the lattice relaxation, the work function, and the electronic density of states, are also studied and discussed in detail. It is pointed out that the O-Pb chemical bonding during surface oxidation displays a mixed ionic/covalent character. Here the ionicity is featured by a charge flow from $\text{Pb}\text{ }6p$ to $\text{O}\text{ }2p$ states, while the covalency is featured by the $\text{Pb}\text{ }6{s}^{2}$ ``lone pair'' effect, which results from hybridization of $\text{Pb}\text{ }6s$ and $\text{O}\text{ }2p$ states.