Dresden 2017 – scientific programme

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O: Fachverband Oberflächenphysik

O 22: Organic-Inorganic Hybrid Systems and Organic Films III

O 22.5: Talk

Monday, March 20, 2017, 18:00–18:15, WIL A317

Global Structure Search for Organic/Inorganic Interfaces: TCNE on Au(111) — •Veronika Obersteiner, Michael Scherbela, Lukas Hörmann, and Oliver T. Hofmann — Institute of Solid State Physics, NAWI Graz, Graz University of Technology, Austria

Structure determination at organic/inorganic interfaces is highly challenging. As individual experiments often convey partial or ambiguous information, computational simulations become increasingly important to aid the interpretation. Here, we demonstrate the power of theoretical polymorph prediction on the example of TCNE (tetracyanoethene) on Au(111).

Predicting polymorphs from first principles is far from trivial. The main challenge is the vast configurational space, i.e. the number of different polymorphs raising exponentially with the number of molecules in the unit cell. Here, we present an approach based on a discretization of the potential energy surface (PES), where we first determine the local adsorption geometries and afterwards span the PES as combinations of these. Dispersion corrected density functional theory is then applied for optimization and to obtain their relative energies.

Applying this approach to TCNE/Au(111), we predict the global minimum to be an ordered triangular structure of slightly tilted upright standing molecules with a substrate adatom in the center. The existence of the adatom cannot be inferred from experimental STM alone [1], but we find it crucial to be able to reproduce the experiment. [1] D. Wegner et al. Nano Letters, 8, 131-135, 2008.