Regensburg 2007 – wissenschaftliches Programm
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SYOE: Symposium Organic Thin Film Electronics: From Molecular Contacts to Devices
SYOE 8: Poster Session SYOE
SYOE 8.6: Poster
Dienstag, 27. März 2007, 18:00–20:00, Poster B
Quantum chemical calculations of PTCDA and NTCDA adsorbates on Ag(110) — •A. Abbasi1,2, R. Scholz1, and M. Schreiber2 — 1Walter Schottky Institut, Technische Universität München — 2Institut für Physik, Technische Universität Chemnitz
The interactions between small Ag(110) clusters and a single NTCDA or PTCDA molecule are investigated with different ab initio techniques. As both Hartree-Fock (HF) theory and density functional theory (DFT) with a gradient-corrected density functional do not contain any correlation energy reproducing the van-der-Waals interaction, we compare these approaches with the fastest numerical technique where the leading term of the van-der-Waals interaction is included, i.e. second order Møller-Plesset theory (MP2). Both HF and DFT result in bended optimized geometries where the adsorbate is interacting mainly via the oxygen atoms, with the core of the molecule repelled from the substrate. Only at the MP2 level, the inclusion of the major part of the attractive van-der-Waals interaction brings the adsorbate back to an arrangement close to parallel to the substrate. With respect to experimental data obtained on Ag(111), the calculated distance between adsorbate and substrate is somewhat smaller, indicating that the open Ag(110) surface interacts more strongly with the organic compounds. This is consistent with the fact that only Ag(110) induces a brickwall unit cell of the adsorbate, a clear sign for a particularly large adsorption energy. The resulting model geometries are analysed in terms of cohesive energy, Mulliken charges, core level shifts, and vibrational properties.