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Zusammenfassung:
The understanding of adsorption and
reactions of (large) organic molecules at metal surfaces plays
an increasingly important role in modern surface science and
technology. Such hybrid inorganic/organic systems (HIOS)
are relevant for many applications in catalysis, light-emitting
diodes, single-molecule junctions, molecular sensors and
switches, and photovoltaics. Obviously, the predictive
modeling and understanding of the structure and stability of
such hybrid systems is an essential prerequisite for tuning their
electronic properties and functions. At present, densityfunctional
theory (DFT) is the most promising approach to
study the structure, stability, and electronic properties of
complex systems, because it can be applied to both molecules
and solids comprising thousands of atoms. However, state-ofthe-
art approximations to DFT do not provide a consistent
and reliable description for HIOS, which is largely due to two
issues: (i) the self-interaction of the electrons with themselves
arising from the Hartree term of the total energy that is not
fully compensated in approximate exchange-correlation functionals,
and (ii) the lack of long-range part of the ubiquitous van der Waals (vdW) interactions. The self-interaction errors
sometimes lead to incorrect description of charge transfer and electronic level alignment in HIOS, although for molecules
adsorbed on metals these effects will often cancel out in total energy differences. Regarding vdW interactions, several promising
vdW-inclusive DFT-based methods have been recently demonstrated to yield remarkable accuracy for intermolecular interactions
in the gas phase. However, the majority of these approaches neglect the nonlocal collective electron response in the vdW energy
tail, an effect that is particularly strong in condensed phases and at interfaces between different materials.
Here we show that the recently developed DFT+vdWsurf method that accurately accounts for the collective electronic response
effects enables reliable modeling of structure and stability for a broad class of organic molecules adsorbed on metal surfaces. This
method was demonstrated to achieve quantitative accuracy for aromatic hydrocarbons (benzene, naphthalene, anthracene, and
diindenoperylene), C60, and sulfur/oxygen-containing molecules (thiophene, NTCDA, and PTCDA) on close-packed and
stepped metal surfaces, leading to an overall accuracy of 0.1 Å in adsorption heights and 0.1 eV in binding energies with respect
to state-of-the-art experiments. An unexpected finding is that vdW interactions contribute more to the binding of strongly bound
molecules on transition-metal surfaces than for molecules physisorbed on coinage metals. The accurate inclusion of vdW
interactions also significantly improves tilting angles and adsorption heights for all the studied molecules, and can qualitatively
change the potential-energy surface for adsorbed molecules with flexible functional groups. Activation barriers for molecular
switches and reaction precursors are modified as well.
