Ab initio total energy calculations using density functional theory with the generalized gradient
approximation have been performed for the chemisorption of oxygen atoms on a Pt$100%-~131!
slab. Binding energies for the adsorption of oxygen on different high-symmetry sites are presented.
The bridge site is the most stable at a coverage of 0.5 ML, followed by the fourfold hollow site. The
atop site is the least stable. This finding is rationalized by analyzing the ‘‘local structures’’ formed
upon oxygen chemisorption. The binding energies and heats of adsorption at different oxygen
coverages show that pairwise repulsive interactions are considerably stronger between oxygen
atoms occupying fourfold sites than those occupying bridge sites. Analysis of the partial charge
densities associated with Bloch states demonstrates that the O–Pt bond is considerably more
localized at the bridge site. These effects cause a sharp drop in the heats of adsorption for oxygen
on hollow sites when the coverage is increased from 0.25 to 0.5 ML. Mixing between oxygen p
orbitals and Pt d orbitals can be observed over the whole metal d-band energy range.