The interaction of thiol molecules with the Au(111) surface was investigated with state-of-the-art first-principles methods. We report theoretical evidence for the existence of a physisorption precursor to chemisorption, in agreement with experiment. The origins of inconsistency in recent studies regarding the adsorption site, geometry, and energetics of CH3S on the Au(111) surface were also investigated. We show that the chemisorption site is between the hollow and bridge sites, with a large molecular tilting angle relative to the surface normal. The molecular structure of the overlayer is coverage dependent, with the molecular tilting angle increasing with decreasing coverage. Increasing chain length up to three carbon atoms affects both the chemisorption energetics and the tilt angle. The inconsistency of tilting angles, reported for the fcc site is found to be a consequence of multiple local minima. The ordered structure of thiol molecules at different coverages was also investigated, confirming the recent experimental findings that the c(4×2) structure model is preferred over (∛×∛)R30°.

State-of-the-art first principles calculations based on density functional theory were performed on CH 3 (CH 2 ) n−1 S-Au(111) systems. We show that the adsorption site of methylthiolate at low coverage on the Au(111) surface is the fcc site, not the hcp site as has been recently reported. Further, we report results for chain length dependency and the electronic structure of the system.The interaction between organic materials and solid surfaces has been extensively studied because of the broad range of industrial applications. 1-4 Self-assembled monolayers (SAMs) hold special interest, because the presence of the thiol group greatly strengthens the molecule-surface interactions, inducing order in the layer. SAMs have important potential applications in industry, such as sensors, transducers, detectors, packaging and insulating layers for integrated circuits, functionalization of surfaces, thin coatings for electrodes, and corrosion inhibition.The long-chain alkane thiols [CH 3 (CH 2 ) n−1 SH, or C n ] form SAMs on the Au(111) surface. Their simplicity, highly ordered structures, and chemical stability make these systems ideal for study with a variety of techniques including atomic force microscopy, 5,6 infrared spectroscopy, 7,8 high-resolution electron-energy-loss spectroscopy, 9 grazing X-ray diffraction, 10 scanning tunneling microscopy (STM), 11-17 scanning probe microscopy, 18 lowenergy electron diffraction (LEED), [19][20][21] He atom diffraction, 22,23 and theory. 25-31 Despite 1

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CO adsorption on the Pt(111) surface is studied using first-principles methods. As found in a recent study [Feibelman et al., J. Phys. Chem. B 105, 4018 (2001)], we find the preferred adsorption site within density functional theory to be the hollow site, whereas experimentally it is found that the top site is preferred. The influence of pseudopotential and exchangecorrelation functional error on the CO binding energy and site preference was carefully investigated. We also compare the site preference energy of CO on Pt(111) with the reaction energy of formaldehyde formation from H 2 and CO. We show that the discrepancies between the experimental and theoretical results are due to the generalized gradient approximation (GGA) treating different bond orders with varying accuracy. As a result, GGA results will contain significant error whenever bonds of different bond order are broken and formed.