Ab Initio Studies of Ag−S Bond Formation during the Adsorption of L‑Cysteine on Ag(111)

摘要

Ab initio studies of Ag−S bond formationnduring the adsorption of L-cysteine on Ag(111) have beennperformed by combining density functional theory with anquantum mechanical model developed in our group. Thenadsorbate−silver bond formation has been investigated bynanalyzing the projected density of states onto the differentnatoms of the molecule and by charge density differencencalculations when the zwitterion radical approaches thensurface. The polar character of the bond can be distinguished.nFor the first time, the coupling constants of the sulfur orbitalsnwith the d and sp bands have been calculated by fitting thendensity of states. The role of the sp bands in the stabilization ofnthe sulfur−silver bond is analyzed. The differences with the catalysis of hydrogen adsorption are discussed. Copper, gold, andnsilver are not good catalysts for the adsorption of hydrogen because of the position of the d bands lying too far below the Ferminlevel. However, the coin metals are excellent for the adsorption of thiols. The reason is that at the equilibrium position the sulfurnatom is much farther from the surface than hydrogen, and thus the interactions with the sp bands stabilize its bond to the surface.