Dresden 2009 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 44: Metal substrates: Adsorption of organic / bio molecules VI
O 44.9: Vortrag
Donnerstag, 26. März 2009, 12:30–12:45, SCH A118
Influence of dispersion interactions on the adsorption geometry of NTCDA on a (110)-oriented silver substrate — •Afshin Abbasi1, Michael Schreiber1, and Reinhard Scholz2 — 1Institut für Physik, Technische Universität Chemnitz, D-09107 Chemnitz, Germany — 2Walter Schottky Institut, Technische Universität München, Am Coulombwall 3, D-85748 Garching, Germany
We investigate the adsorption of NTCDA on Ag(110) with second-order Møller-Plesset perturbation theory (MP2) and density functional theory (DFT), using rigid metal clusters of different size as a model for the substrate. In each method, the adsorption geometry depends only weakly on the size of the metal cluster, but both microscopic approaches differ significantly: MP2 gives a nearly flat adsorbate, whereas the lack of dispersion interaction in DFT results in a strongly bended geometry, placing the aromatic core at a much larger distance from the topmost substrate layer with respect to the oxygen groups. Irrespective of the microscopic approach, the carboxylic oxygens interact more strongly with the substrate than the anhydride oxygens, placing them about 0.2 Å closer to the topmost silver layer. On the largest substrate cluster containing 34 silver atoms in three consecutive crystal planes, MP2 places the carbon atoms at an average height of 2.57 Å above the topmost silver layer, about 0.3 Å closer than in the strongly bended geometry geometry obtained with DFT. From these findings, we conclude that the chemisorption geometry of NTCDA on Ag(110) cannot be quantified without the dispersion interactions included at the MP2 level.