CO chemisorption at metal surfaces and overlayers.

A database of ab initio calculations of the chemisorption energy of CO over Ni(111), Cu(111), Ru(0001), Pd(111), Ag(111), Pt(111), Au(111), Cu3Pt(111), and some metallic overlayer structures is presented. The trends can be reproduced with a simple model describing the interaction between the metal d states and the CO 2p p and 5s states, renormalized by the metal sp continuum. Our model rationalizes the results by Rodriguez and Goodman [Science 257, 897 (1992)] showing a strong correlation between the CO chemisorption energy and the surface core level shift. Over the past three decades the field of surface science has produced a series of accurate spectroscopical techniques that can provide detailed information about the electronic structure at surfaces [1]. It would be extremely useful if spectroscopic data could also be used directly to give information about the chemical activity of the surface. This would open up new possibilities in the future search for, e.g., more efficient catalysts. Recently, Rodriguez and Goodman [2] have established a spectacular correlation between spectroscopical data (surface core level shifts) and the chemisorption energy of CO on a series of metal surfaces and overlayers. If such an approach can be generalized, we would have a means of predicting the chemical activity of surfaces based on the surface electronic properties alone. In the present Letter, we discuss the physics of CO adsorption over metal surfaces and overlayers by presenting an extensive ab initio database of CO chemisorption energies calculated within density functional theory (DFT) using the generalized gradient approximation (GGA). We demonstrate that the trends in the database can be understood using a simple two-level model describing the coupling of the CO 5s and 2p p states to the metal d va