Benzene Adsorbed on Metals: Concerted Effect of Covalency and van der Waals Bonding

TL;DR

This study investigates how van der Waals interactions influence benzene adsorption on various metal surfaces, revealing their significant role even in covalent bonding scenarios and improving theoretical predictions.

Contribution

It demonstrates that advanced vdW-inclusive DFT methods accurately model benzene adsorption across different metal surfaces, bridging the gap between weak and strong binding regimes.

Findings

vdW forces significantly affect covalent benzene-metal bonds

adsorption barriers vanish when vdW interactions are included

methods match experimental adsorption data

Abstract

The adsorption of aromatic molecules on metal surfaces plays a key role in condensed matter physics and functional materials. Depending on the strength of the interaction between the molecule and the surface, the binding is typically classified as either physisorption or chemisorption. Van der Waals (vdW) interactions contribute significantly to the binding in physisorbed systems, but the role of the vdW energy in chemisorbed systems remains unclear. Here we study the interaction of benzene with the (111) surface of transition metals, ranging from weak adsorption (Ag and Au) to strong adsorption (Pt, Pd, Ir, and Rh). When vdW interactions are accurately accounted for, the barrier to adsorption predicted by standard density functional theory (DFT) calculations essentially vanishes, producing a metastable precursor state on Pt and Ir surfaces. Notably, vdW forces contribute more to the binding of covalently bonded benzene than they do when benzene is physisorbed. Comparison to experimental data demonstrates that some of the recently developed methods for including vdW interactions in DFT allow quantitative treatment of both weakly and strongly adsorbed aromatic molecules on metal surfaces, extending the already excellent performance found for gas-phase molecules.