Trends in Adsorption Characteristics of Benzene on Transition Metal Surfaces: Role of Surface Chemistry and van der Waals Interactions

The accurate description of interface characteristics between organic molecules and metal surfaces has long been debated in theoretical studies. A well-founded description of interface geometry and adsorption energy is highly desirable for these hybrid inorganic/organic interfaces. Using first principles calculations with the inclusion of five van der Waals functionals (vdW-DF family), benzene (C6H6) adsorption on seven transition metal surfaces is studied to explore the performance of these vdW functionals under varying surface chemistry. Our results reveal that vdW interactions are crucial for an accurate description of bonding on transition metal substrates. We find that vdW interactions increase adsorption energy on coinage metal surfaces (Au, Ag, Cu) by about 0.7 eV, while they lead to even larger increases in the adsorption energies on the reactive transition metal surfaces (Pd, Pt, Rh, Ni). Our calculations also reveal that changes in adsorption energies stemming from vdW functionals show significant variation, and can be grouped. We find the adsorption energies and heights on the reactive transition metal surfaces obtained using vdW-DF and vdW-DF2 functionals to differ significantly from those of the opt-type functionals, revealing the intrinsic strong repulsion character at short ranges for the former functionals. A simple comparison between experimentally determined adsorption energies (averaged) and those of computed suggests that optPBE and optB88 functionals show systematically good agreement. The information acquired from our analysis on the performance of these functionals can be used as a basis for further refinement of these functionals for the adsorption on metal surfaces with varying chemistry.