LAUSR

Density functional theory has been used to investigate the adsorption and dissociation of 5-hydroxy-3-hexanediol-1,4-naphthaquinone (Jug-C4-thiol) at a coverage of p(4 × 4) on a Au(111) surface. Both physisorption and chemisorption processes are investigated. For each process, the surface energy potential is explored by an exhaustive test of the adsorption site. The most favorable site is found to be face-centered cubic. The adsorption energies are less than − 0.20 eV in the case of physisorption, while they range from − 1.70 to − 1.92 eV for chemisorption. The effect of the naphthoquinone function is negligible in the adsorption process. The alkyl chain inhibits electron delocalization between the surface and the conjugated head of the molecule. Analysis of the bonding shows the formation of two ionocovalent bonds between the sulfur and the gold atoms. The thermodynamics and kinetics of S–H bond dissociation are studied. The results reveal that adsorption involves a dissociation path in which a hydrogen atom moves to the most neighboring site and a hydrogen atom migrates to its most stable site. The maximum barrier energy of the first step is less than 2.7 eV while the migration barrier does not exceed 0.5 eV.