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CO adsorption on close-packed transition and noble metal surfaces: trends from ab initio calculations

We have studied the trends in CO adsorption on close-packed metal surfaces: Co, Ni, Cu from the 3d row, Ru, Rh, Pd, Ag from the 4d row and Ir, Pt, Au from the 5d row using density functional theory. In particular, we were concerned with the trends in adsorption energy, geometry, vibrational properties and other parameters derived from the electronic structure of the substrate. The influence of specific changes in our set-up, such as choice of the exchange correlation functional, the choice of pseudopotential, size of the basis set and substrate relaxation, has been carefully evaluated. We found that, while the geometrical and vibrational properties of the adsorbate–substrate complex are calculated with high accuracy, the adsorption energies calculated with the gradient-corrected Perdew–Wang exchange–correlation energies are overestimated. In addition, the calculations tend to favour adsorption sites with higher coordination, resulting in the prediction of the wrong adsorption sites for the Rh, Pt and Cu surfaces (hollow instead of top). The revised Perdew–Burke–Erzernhof functional (RPBE) leads to lower (i.e. more realistic) adsorption energies for transition metals, but to the wrong results for noble metals—for Ag and Au, endothermic adsorption is predicted. The site preference remains the same. We discuss trends in relation to the electronic structure of the substrate across the periodic table, summarizing the state-of-the-art of CO adsorption on close-packed metal surfaces.