CO adsorption on the CO-precovered Pt(111) surface characterized by density-functional theory

Abstract

Ab initio density-functional investigations of the gradual adsorption of increasing amounts of CO on partially precovered Pt(111) surfaces are presented. Our calculations show that up to precoverages as high as 0.5 monolayer (ML) CO, the adsorption energy is minimally influenced by lateral interactions and that adsorption of additional CO molecules remains an unactivated process. The saturation coverage is estimated to be $\ensuremath{\sim}0.67$ ML. Beyond this limit the adsorption energies are strongly reduced and substantial barriers against further adsorption are built up. For the high-coverage limit, we have examined several adsorption geometries proposed in the literature as well as a novel configuration. Energetic considerations, the calculated adsorption geometries, and the analysis of the calculated frequency spectra all favor a model with the $c(\sqrt{3}\ifmmode\times\else\texttimes\fi{}3)$ periodicity as proposed on the basis of the experimental data.