n-alkyl thiol head-group interactions with the Au(111) surface

State-of-the-art first-principles calculations based on density-functional theory were performed on ${\mathrm{CH}}_3({\mathrm{CH}}_2{)}_{n-1}\mathrm{S}-\mathrm{Au}\mathrm{}(111)\mathrm{}$ systems. We show that the adsorption site of methylthiolate at a range of coverages on the Au(111) surface is the fcc site, not the hcp site as has been recently reported. Further, we report that increasing alkane chain length enhances the fcc site preference. Study of the electronic structure of the system underscores the importance of sulfur $3d$ orbitals to thiol chemisorption.