Dresden 2009 – scientific programme

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O: Fachverband Oberflächenphysik

O 18: Metal substrates: Adsorption of organic / bio molecules III

O 18.9: Talk

Tuesday, March 24, 2009, 12:30–12:45, SCH A118

Molecular Switches at Surfaces: The Role of Van Der Waals Interactions — •Erik McNellis, Joerg Meyer, and Karsten Reuter — Fritz-Haber-Institut, Faradayweg 4-6, 14195 Berlin

Molecules that by external stimuli may be reversibly switched between different defined states are envisioned as a key component of a future molecular nanotechnology. For the latter, it is particularly the molecular function when the switch is stabilized at a solid surface that is of key interest. Using density-functional theory (DFT) with a gradient-corrected (GGA) functional we carry out a detailed characterization of the metastable structures of the prototypical molecular switch azobenzene at close-packed coinage metal surfaces. We obtain a range of switch-surface interactions that goes from weak physisorption at Au(111) to a reversal in the stability of the gas-phase cis and trans molecular conformations at Cu(111). In view of the known inadequacies of present-day GGA functionals in the description of long-range van der Waals interactions, we check on these findings considering corrections from semi-empirical pair potential schemes. While corrections to the gradient are small enough to leave adsorbate geometries essentially unchanged, the obtained adsorption energy corrections are substantial, in certain cases significantly altering the pure DFT picture. We discuss this, and the discomforting differences obtained between the employed semi-empirical schemes in the greater context of molecular adsorption at metal surfaces.