Oxygen adsorption on Cu(100): First-principles pseudopotential calculations

We have studied the adsorption characteristics of atomic and molecular oxygen, incident on the Cu(100) surface. Our pseudopotential first-principles calculations yield trajectories for the ${\mathrm{O}}_2$ molecule without dissociation barriers at the entrance channel. We discuss the energetics of the ${\mathrm{O}}_2$ adsorption and dissociation in terms of the elbow plots which are two-dimensional cuts of the full six-dimensional potential-energy surface. The top site is found to be the most reactive one while at the fcc site molecular adsorption takes place. The adsorption energies at horizontal configurations of the ${\mathrm{O}}_2$ molecule are found to be larger than those at the vertical configurations. The local densities of states reveal differences between the sites with direct dissociative adsorption and the ones with molecular precursor states. We also discuss the interactions between O and Cu atoms adsorbed at the hollow sites on Cu(100), and the corresponding diffusion barriers.

Figure 1

Configurations of the ${\mathrm{O}}_2$ molecule (solid circles) on Cu(100) for which the elbow plots were calculated. Top sites, configurations 1–2; fcc sites, configurations 3–4; bridge sites, configurations 5–6. The larger and smaller circles denote Cu atoms at the topmost and second layer, respectively.

Figure 2

Cuts through the six-dimensional potential-energy surface for ${\mathrm{O}}_2$ on Cu(100) calculated with the spin-averaged formalism. $z$ is the distance of center of mass of the ${\mathrm{O}}_2$ molecule from the surface (in Å) and $d$ is the bond length of the ${\mathrm{O}}_2$ molecule (in Å). Left panel, top site (top, configuration 1; bottom, configuration 2); middle panel, hollow site (top, 3; bottom, 4); right panel, bridge site (top, 5; bottom, 6). See text for details.

Figure 3

Cuts through the six-dimensional potential-energy surface for ${\mathrm{O}}_2$ on Cu(100) calculated with the spin-polarized formalism. $z$ is the distance of the center of mass of the ${\mathrm{O}}_2$ molecule from the surface (in Å), and $d$ is the bond length of the ${\mathrm{O}}_2$ molecule (in Å). Left panel, top site (top, configuration 1; bottom, configuration 2); right panel, hollow site (top, configuration 3; bottom, configuration 4). See text for details.

Figure 4

LDOS for the ${\mathrm{O}}_2$ molecule above (a) top (configuration 2) and (b) fcc site (configuration 4). The distance of the molecule from the surface is about $1.7\mathrm{\AA }$ which in the case of the fcc site is approximately the equilibrium distance of the molecule from the surface. Solid line represents $d$-DOS for the surface Cu atom which is the nearest neighbor of the O atoms in the molecule, dotted line is $p$-DOS for one of the O atoms, and dashed line $d$-DOS for a Cu atom on clean Cu(100).

Figure 5

Configurations and diffusion processes (listed in Table ) for the adatoms and small clusters of Cu and O on Cu(100). Illustrated is the initial configuration of the adatom cluster and the arrows indicating the corresponding jump.