Adsorption of ethylene on the Ag(001) surface

We report on a set of ab initio calculations, performed within density-functional theory, aimed at characterizing the adsorption of ethylene on the Ag(0 0 1) surface. Our results indicate that the binding of the adsorbate to the substrate is rather weak and that the molecular geometry is correspondingly almost unaffected by adsorption. In spite of this, we have also found a substantial amount of hybridization between ethylene pi and silver d(z2) states. The apparent contradiction between weak binding and strong hybridization is due to a substantial occupation of anti-bonding hybrid orbitals, which lowers the strength of the chemical bond. To better understand the role of metal d states in the adsorbate-substrate bond, we have also performed similar calculations for ethylene adsorbed on Al(0 0 1), and compared the corresponding results. Our analysis shows that no strong chemical bond between C2H4 and a clean Ag(00 1) surface exists. Preliminary results indicate that the strength of the bond is Substantially increased by steps, adatoms, or possibly other imperfections of the substrate. (C) 2002 Elsevier Science B.V. All rights reserved.