Structure and Energetics of Benzene Adsorbed on Transition-Metal Surfaces: Density-Functional Theory with Screened van der Waals Interactions

The adsorption of benzene on metal surfaces is an important benchmark system for more complex hybrid inorganic/organic interfaces. Here, the recently developed DFT+vdW$\rm^{surf}$ method (density-functional theory including screened van der Waals (vdW) interactions) [1] is used to study the structure and energetics of benzene on transition-metal surfaces (Cu, Ag, Au, Pd, Pt, Rh, and Ir). Benzene adsorbs in a planar configuration at coinage metal surfaces, with almost zero distortion and a flat potential-energy surface. In contrast, benzene is strongly bound to the (111) surface of Pd, Pt, Rh, and Ir, and located at the bridge-30$^\circ$ site. The vdW interactions significantly enhance the binding energy by more than 0.75 eV for all metals. The screening of the vdW energy plays a critical role in coinage metals, shortening the equilibrium distance by 0.2 {\AA}, and lowering the binding energy by 0.25 eV. The validity of our results is confirmed by comparison with calculations using the random-phase approximation including renormalized single excitations (EX+cRPA+rSE scheme [2]), and the experimental data from temperature-programmed desorption and calorimetry measurements. [1] V. G. Ruiz-L\'{o}pez et al., submitted. [2] X. Ren et al., Phys. Rev. Lett. 106, 153003 (2011).