Many-body dispersion effects on the binding of TCNQ and F4-TCNQ with graphene

Predictive modeling and understanding of binding of organic molecule-decorated graphene is an essential prerequisite for tuning their electronic and magnetic properties. Many-body dispersion (MBD) interactions are known to contribute significantly to the binding of condensed matters, but the role of MBD energy in self-assembled organic monolayers on epitaxial graphene remains largely unexplored. Here, by using the state-of-the-art DFT + MBD method, we for the first time investigate model π-π adsorption systems that are composed of two typical acceptor molecules, TCNQ and F4-TCNQ, and graphene sheets. The computed binding energies from the DFT + MBD method are consistently smaller than those from the pairwise-based van der Waals (vdW) inclusive method, such as DFT + vdW, due to the accurate capture of both electrodynamic screening and many-body effects in the former case. Notably, many-body effects contribute more to the low-coverage adsorption systems than they do when the substrate is highly covered by the adsorbates. This somewhat counter-intuitive result is attributed to the fact that each molecule contributes less to the polarization of the hybrid interface at high coverage.

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