Automated Process Exploration The initial oxidation of Pd surfaces generally proceeds by O decoration of step edges, which then serves as nucleus for the transformation to surface oxides. We exemplarily explore the underlying elementary processes using the Pd(410) vicinal, which exposes four atom row wide Pd(100) terraces that are separated by (110) steps. Cast into a periodic boundary condition supercell in which the surface unit-cell is extended three times along the step edge and twice across the step edges to cover two subsequent terraces, cf. Fig. , this leads to a system size with enough structural flexibility to even allow for O-induced breaking of the step edge and step bunching (see below), but for which comparison with DFT calculations is still manageable. While the more open (110) steps seem more prone to oxidation anyway, we nevertheless note that attempts to explore processes for the alternative (111) steps, as e.g. exposed by (11N ) vicinals, suffered from finite-size effects in corresponding supercell setups. There APE identifies numerous unphysical low-barrier processes involving infinite row shifts along the step edge. Similar processes are also found in the (410) supercell, but due to the different step geometry their end states result in undercoordinated Pd atoms with a corresponding sizable energy penalty.