Zeitschriftenaufsätze

The interaction of PTCDA with Ag(110) is analysed with second order Møller-Plesset perturbation theory (MP2), including the main part of the dispersion interactions at an ab initio level. On rigid substrate clusters, the optimized adsorbate geometry consists of a nearly flat perylene core, surrounded by carboxylic oxygens closer to the substrate, but with anhydride atoms at a larger height. The average height of the carbon core is found at 2.68 Å, in excellent agreement with the value of 2.59 Ädetermined in recent X-ray standing wave measurements. In sharp contrast to the rather flat MP2 geometry, the lack of dispersion interactions in density functional theory (DFT) results in an unrealistic bent adsorbate geometry. The calculated core level shifts and the vibrational fingerprint reproduce the observed trends.