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Theoretical study of the CO adsorption on the (100) surface of the face-centered cubic d-block transition metals

Abstract:

The interaction of a CO molecule with the (100) surface of the fcc d-block transition metals is analyzed by the topology of the Laplacian of the electronic charge density -▽<sup>2</sup> ρ. This analysis shows that the atomic graph for the top atoms is an octahedron that exposes, outside the (100) surface, a vertex V<inf>top</inf> with a local maximum of charge, and four faces F<inf>top</inf> with a local minimum. The corresponding graph for the second-layer atoms is also an octahedron that exhibits a vertex V<inf>sec</inf> outside the surface. Atomic graphs for the CO molecule show that the carbon atom has a non-bonded vertex C<inf>nb</inf>, and a torus C<inf>torus</inf> of charge depletion perpendicular to the C - O bond direction. Laplacian topology predicts CO perpendicular orientation in bridge- or top-sites. The bridge-site involves attractive interactions with two atoms of the surface: face (metal top atom)-vertex (C atom)-face (metal top atom). The top-site involves the attractive interaction vertex (C atom)-face (metal top atom). Attractive interaction between the surface and only one atom of the CO molecule rules out dissociation and predicts molecular adsorption.