Abstract
The adsorption of benzene on metal surfaces is an important benchmark system for hybrid inorganic/organic interfaces. The reliable determination of the interface geometry and binding energy presents a significant challenge for both theory and experiment. Using the Perdew–Burke–Ernzerhof (PBE), PBE + vdW (van der Waals) and the recently developed PBE + vdWsurf (density-functional theory with vdW interactions that include the collective electronic response of the substrate) methods, we calculated the structures and energetics for benzene on transition-metal surfaces: Cu, Ag, Au, Pd, Pt, Rh and Ir. Our calculations demonstrate that vdW interactions increase the binding energy by more than 0.70 eV for physisorbed systems (Cu, Ag and Au) and by an even larger amount for strongly bound systems (Pd, Pt, Rh and Ir). The collective response of the substrate electrons captured via the vdWsurf method plays a significant role for most substrates, shortening the equilibrium distance by 0.25 Å for Cu and decreasing the binding energy by 0.27 eV for Rh. The reliability of our results is assessed by comparison with calculations using the random-phase approximation including renormalized single excitations, and the experimental data from temperature-programmed desorption, microcalorimetry measurements and low-energy electron diffraction.
Highlights
It has already been shown that the DFT+vdWsurf method yields excellent agreement with experiments for a variety of atoms and molecules adsorbed on metal surfaces.[56,75,76,77,78]
We will provide more detailed analysis for benzene adsorbed on transition-metal surfaces, in order to further clarify the critical role of van der Waals (vdW) interactions in the prediction of adsorption structures and energetics, and to deepen our understanding of the nature of bonding for the adsorption of aromatic molecules
DFT calculations including the longrange contributions to the vdW interactions and collective response of the substrate electrons within the metal bulk were carried out to investigate the structure and energetic properties of benzene adsorbed on transitionmetal surfaces
Summary
Hybrid inorganic/organic systems (HIOS) have attracted considerable interest because they could be used to tailor the electronic, optical, and magnetic properties of functional materials.[1,2,3,4,5] A wide range of HIOS has been created through the self assembly of organic molecules on diverse substrates.[6,7,8] Special attention has been paid to the adsorption of benzene (Bz) on transition-metal surfaces.[9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30] Bz is a fundamental aromatic molecule and more importantly, the prototype for an entire class of aromatic hydrocarbons.[30,31,32,33] Such aromatic hydrocarbons are among the principal constituents of biochemical and petroleum industries, and they are widely used in the production of plastics, fibres, and rubbers. None of the mentioned methods account for nonlocal (inhomogeneous) collective (many-body) effects, which are important for extended systems, in particular metals.[73] Recently, some of us have developed a method to calculate the vdW energy for atoms and molecules on surfaces by using the combination of the DFT+vdW approach for intermolecular interactions with the Lifshitz-Zaremba-Kohn (LZK) theory[74] for the non-local collective response of a metal substrate. This method will be referred to as “DFT+vdWsurf ” in the following.
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