In principle, the field changes the charge state on the surface considerably (see Figure ), and since different adsorption geometries are differently affected by the field, one could expect that the (relative) vibrational energy changes with the field. While this is certainly the case in general, for our example of TCNE on Cu(111) we show in the Supporting Information that the charge state (coincidentally) does not play a noticeable role. Furthermore, we also find that the change of the zero-point energy of TCNE molecules with the electric field is small regardless of molecule orientation relative to the field, as we show in the Supporting Information. Thus, for the present work, we, therefore, neglect the contributions from vibrations of molecules on the surface as well, i.e., G sys (p, T , F ) ≈ E ML sys (F ).