To analyze how the adsorption geometries change in the presence of an electric field, we again relaxed all 11 previously obtained geometries in the presence of homogenous electric fields applied perpendicular to the Cu surface, using field strengths between -3 V nm -1 and +3 V nm -1 . The sign of the field denotes the direction. Positive values correspond to a field whose field lines would point towards the interface for a positive test charge. We note that field strengths of this magnitude are larger than what is used in typical crystallization experiments, but they can, in principle, be experimentally realized, e.g., in STM junctions or in optical experiments. Moreover, such large field strengths are also considered in other theoretical works. After the relaxation, we observe that the adsorption geometries change only very little, with none of the atoms moving by more than 0.07 Å. Consequently, also the energy change associated with that geometry adaption is almost negligible, being less than 10 meV for all geometries.