Density functional theory studies on the adsorption of 4-methylbenzenethiol and 4-ethylbenzenethiol molecules on Au (111) surface

The nondissociative and dissociated adsorptions of 4-methylbenzenethiol (4-MBT) and 4-ethylbenzenethiol (4-EBT) on Au(111) surface were studied by applying the first-principles method based on density functional theory. The effects of coverage and vdW interactions on adsorptions were investigated. Adsorption energies and tilt angles of both 4-MBT and 4-EBT decrease with the increase of the coverage, and vdW interactions can affect the adsorption configuration and energy. More importantly, in the case of 4-EBT adsorption, we have studied the effects of ethyl group's orientation on the adsorption configuration and energy. Calculation results show that ethyl group's orientation has little effect on the adsorption energy, but changes the tilt angle by around 7°. Our calculations provide a deeper elucidation of the observed adsorption configuration for 4-EBT on Au(111).