Binding Energy Simulations. To calculate the optimum molecule-molecule and molecule-surface binding distances, we used DFT and the counterpoise method, which removes basis set superposition errors (BSSE). The optimum binding distance z is defined as either the optimum TEMPO-TEMPO or TEMPO-HOPG distance. If one of the entities (TEMPO or HOPG) is defined as entity A and the TEMPO or graphite as entity B, then the ground-state energy of the total system is calculated using SIESTA and is denoted E AB AB . The energy of each entity is then calculated on a fixed basis, which is achieved in SIESTA using ghost atoms, (basis set functions which have no electrons or protons). Hence, the energy of the individual TEMPO or graphite in the case of the fixed basis is defined as E A AB and for the TEMPO or graphite as E B AB . The binding energy is then the difference between the isolated entities and their total energy when placed a distance 𝑧 apart, which is calculated using the following equation: Binding Energy = 𝐸 𝐴𝐵 𝐴𝐵 -𝐸 𝐴 𝐴𝐵 -𝐸 𝐵 𝐴𝐵 , as shown in Figs.