Modeling Intercalated Graphene/O/Ir(111) for Organic Molecular Thin Films

Organic charge transfer complexes (CTCs) are commonly grown on decoupled intercalated graphene (Gr) to avoid interference of the metallic substrate on their electronic properties. CTCs can feature different structural phases [1], but simulations are needed to resolve film morphologies. The complex substrate and large configurational space makes global ab-initio structure search intractable. In this study, we approximate the intercalated substrate using freestanding Gr with modified electronic structure. We confirm our Gr model with molecular adsorbates, which we identify with Bayesian optimization structure search (BOSS) [2] and density-functional theory (DFT).

We demonstrate this approach with F₄TCNQ and TTF on Gr/O/Ir(111). We build a surrogate adsorption energy surface (AES) with BOSS and DFT as a function of molecular orientation and translations. In the AES minima, we identify 3 stable configurations of F₄TCNQ and 5 of TTF, and find new structures in addition to previously reported configurations. Our study shows that complex intercalated substrates may be approximated with charged freestanding Gr, which can facilitate exhaustive structure search of CTCs.

[1] A. Kumar et al., ACS Nano 2021, 15, 6, 9945.

[2] M. Todorović et al., npj Comput. Mater. 2019, 5, 35.