The different changes in both E bond and E geom have multiple origins. As explained above, E geom captures the reorientation and deformation of the molecule and the energy of the resulting adsorbate dipole in the field. The reorientation energy is rather small for standing ChemRxiv adsorption geometries because the polarizability is very similar for both molecular axes that lie in the π-plane of the molecule (x-axis and y-axis). Standing molecules also deform very little during adsorption, resulting in a small deformation energy and adsorbate dipole. As a result, E geom is small for standing adsorption geometries. For lying molecules, the situation is quite different. Lying molecules adsorb with the z-axis of the molecule perpendicular to the substrate surface (i.e., in direction of the field). The polarizability along the z-axis is much different than that along the x-axis, yielding a substantial reorientation energy. Furthermore, the molecule deforms significantly during adsorption. In the absence of an electric field E geom corresponds entirely to the deformation energy. As can be seen in Figure at F = 0 V nm -1 , the difference in deformation energy between the lying and the standing adsorption geometry amounts to approximately 0.5 eV. Thus, it accounts for most of the difference in E geom between the lying and the standing geometry. The strong deformation lying molecules experience also gives rise to a large adsorbate dipole. Both reorientation and the potential energy of the adsorbate dipole in the field give rise to strongly field-dependent contributions to E geom . As a result, E geom is significantly impacted by the field for lying but hardly for standing.