Azobenzene at coinage metal surfaces: Role of dispersive van der Waals interactions

We use different semiempirical dispersion correction schemes to assess the role of long-range van der Waals interactions in the adsorption of the prototypical molecular switch azobenzene (C6H5-N-2-C6H5) at the coinage metal surfaces Cu(111), Ag(111), and Au(111). Compared to preceding density-functional theory results employing a semilocal exchange and correlation functional we obtain partly sizable changes in the computed adsorption geometry and energetics. The discomforting scatter in the results provided by the different schemes is largely attributed to the unknown form of the damping function in the semiempirical correction expression. Using the congeneric problem of the adsorption of benzene as a vehicle to connection with experiment, we cautiously conclude that the account of dispersive interactions at the metal surfaces provided by the various schemes is in the right ballpark, with the more recent, general schemes likely to overbind.