Regensburg 2019 – scientific programme
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O: Fachverband Oberflächenphysik
O 98: Organic Molecules on Inorganic Substrates VII
O 98.4: Talk
Friday, April 5, 2019, 11:15–11:30, H17
Understanding Charge Transfer of TCNE on Cu(111) using Structure Search — •Alexander T. Egger1, Lukas Hörmann1, Andreas Jeindl1, Milica Todorović2, Patrick Rinke2, and Oliver T. Hofmann1 — 1Institute of Solid State Physics, TU Graz, Austria — 2Department of Applied Physics, Aalto University, Finland
TCNE (tetracyanoethene) is known as a strong electron acceptor that forms charge-transfer complexes upon adsorption on metals. On Cu(111), it has been claimed [1] that this charge transfer includes the second layer, whereby molecules of this second layer are singly charged.
To understand these charge-transfer complexes, knowing the atomic structure of the adlayers is mandatory. However, the number of possible geometries is immense and an accurate describtion of charge transfer requires dispersion-corrected density functional theory (DFT), which – due to its computational costs – inhibits a brute-force search. Using two complimentary machine-learning-based approaches [2,3] allows us to predict the adsorption energies of an exhaustive set of coarse-grained candidate structures at reasonable computational cost while preserving the numerical accuracy of the electronic structure calculations.
Our studies reveal that for TCNE on Cu(111) charge transfer to the second layer is in fact negligible. Instead, a phase transition occurs in the first layer: At high coverage adsorbate molecules flip from face-on to edge-on orientation explaining the observed singly-charged species.
[1] Erley et al., J. Phys. Chem., 91.11
[2] Hörmann et al., arXiv:1811.11702
[3] Todorović et al., arXiv:1708.09274