  Halogenated aromatic molecules assemble on surfaces forming both hydrogen and
halogen bonds. Even though these systems have been intensively studied on flat
metal surfaces, high-index vicinal surfaces remain challenging, as they may
induce complex adsorbate structures. The adsorption of 2,6-dibromoanthraquinone
(2,6-DBAQ) on flat and stepped gold surfaces is studied by means of van der
Waals corrected density functional theory. Equilibrium geometries and
corresponding adsorption energies are systematically investigated for various
different adsorption configurations.~It is shown that bridge sites and step
edges are the preferred adsorption sites for single molecules on flat and
stepped surfaces, respectively. The role of van der Waals interactions, halogen
bonds and hydrogen bonds are explored for a monolayer coverage of 2,6-DBAQ
molecules, revealing that molecular flexibility and intermolecular interactions
stabilize two-dimensional networks on both flat and stepped surfaces. Our
results provide a rationale for experimental observation of molecular carpeting
on high-index vicinal surfaces of transition metals.
