As model system for our investigations, we use the conjugated organic acceptor molecule tetracyanoethylene (TCNE) on a Cu(111) surface. This interface system is ideal for our study because its surface chemistry is fairly well characterized (in absence of electric fields), both experimentally and through simulations. Different polymorphs of TCNE on Cu(111) have been shown to exhibit substantially different properties such as the work function, which varies by up to 3 eV between polymorphs. TCNE is known to bond to the surface through a Blyholder-like interaction, comprising charge-donation from the metal into the molecular LUMO and back-donation from the molecular π-system to the surface. Importantly, the resulting molecule-substrate interaction is strongly different for different adsorption geometries. Furthermore, like most conjugated organic molecules, TCNE is a molecule with different polarizabilities along different molecular axes.