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CPP: Chemische Physik und Polymerphysik

CPP 27: POSTER Polymer Physics and Materials

CPP 27.30: Poster

Donnerstag, 30. März 2006, 17:00–19:00, P2

Chemisorption of PTCDA on Ag(110): A quantum chemical study — •Afshin Abbasi, Michael Schreiber, and Reinhard Scholz — Institut für Physik, Technische Universität Chemnitz

Experimental studies of PTCDA monolayers on Ag(110) have revealed an adsorption geometry where each molecule is placed on top of 12 substrate atoms [1]. In the present work, we investigate a non-periodic approximant of this interface, including one PTCDA molecule and one or two layers of silver. Both in Hartee-Fock and DFT calculations, the anhydride oxygen atoms experience a strong interaction with the substrate, resulting in a bended geometry with an Ag-O bond length of about 2.4 Å. Several orbitals delocalized over the molecule and the topmost substrate layer result in a large positive net charge of the adsorbate. As most of the negative charge in the topmost layer of the substrate resides below the positively charged perylene core, the Coulomb interaction between substrate and adsorbate contributes a substantial part to the total binding energy.

The calculated adsorption geometry is analysed in terms of the chemical hardness of the electronic orbitals, electronic excitations, and the infrared activity of the molecule along the substrate normal.

[1] C. Seidel, J. Poppensieker, and H. Fuchs, Surf. Sci. 408, 223 (1998); M. Böhringer, W. D. Schneider, K. Glöckler, E. Umbach, and R. Berndt, Surf. Sci. 419, L 95 (1998).