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The role of many-body effects at adsorbate-metal interfaces is a crucial – but often overlooked – factor in designing materials for spintronic and electrocatalytic applications. Correlation-driven modifications to the electronic structure of ferromagnetic surfaces can promote surface-adlayer interactions and enhance surface reactivity [1,2]. A prime example is the oxygen-passivated Fe(100) surface, where a chemisorbed layer of oxygen leads to spin-dependent band broadening, narrowing of Fe d-bands near the Fermi energy, and a reduction in the exchange splitting [3].
Modelling the influence of these modifications on adsorbates is a theoretical challenge. Such systems are usually poorly described by standard density functional theory (DFT), while the size of the unit cell currently renders more advanced approaches like dynamical mean-field theory computationally prohibitive. Interestingly, we found that a tailored DFT+U approach with a negative effective on-site interaction ($U_{eff}$ = −3.1 eV) captures the experimentally observed electronic structure surprisingly well. In specific, we present the analysis of three different system, namely Fe-O covered with a monolayer of MgO, Pentacene, and fluorinated TCNQ. We show that the unconventional use of DFT+U is able to reproduce important interface properties, such as the energetic overlap between metal d-states and adlayer orbitals, which governs the transition between physisorption and chemisorption. Our theoretical findings are confirmed by momentum-resolved photoemission orbital tomography and scanning tunnelling spectroscopy data.
[1] Cao, A. and Nørskov, J.K.. ACS Catal., 2023, 13, 3456.
[2] Zhang, K., et al. Science, 2024, 383, 1357.
[3] Janas, D.M., et al. Adv. Mater., 2023, 35, 2205698.