While the calculation of the slab energy in the electric field is straightforward, for a TCNE molecule in gas phase the anisotropic polarizability must be considered. The energy of the molecule in the field varies with its orientation with respect to the field. At zero temperature it, therefore, orients itself such that the molecular axis with the highest polarizability is aligned with the direction of the electric field. In case of TCNE, this is the x-axis in Figure (parallel to the C --C bond). This fact is important, as it means that the molecule must potentially reorient in the field to adsorb on the surface (e.g., for the lying category). Additionally, the geometry of the molecule is deformed during adsorption, which (i) requires energy by itself, and (ii) gives rise to an adsorption geometry specific adsorbate dipole (hereafter called adsorbate dipole). This adsorbate dipole also changes in magnitude as the molecule is polarized by the electric field. We denote the component of the adsorption energy associated with all these geometric changes (reorientation, deformation, adsorbate dipole in the electric field) as E geom . It is obtained by calculating the energy difference between the deformed and the relaxed, optimally aligned adsorbate molecule in vacuum with the electric field applied. The remaining part of the adsorption energy, which stems from the bonding of the molecule to the substrate is denoted as E bond :