As an approximation for the complete molecular layer, we simulated two TEMPO molecules (dimer) on the graphite surface. Our calculations reveal that the TEMPO-TEMPO interaction is substantially higher compared to the TEMPO-graphite interaction (Figures ). By computing the total energy of a TEMPO-TEMPO dimer as a function of their separation, we find that antiparallel orientations are always the lowest energy arrangement (Figures and), and that an upright antiparallel geometry is the most favourable. This is due to the upright arrangement maximising the dipole-dipole interaction between molecules. This was tested by artificially increasing the TEMPO-TEMPO spacing such that the molecules become well separated and the dipoledipole interaction is reduced. In this case, the molecules return to a tilted orientation similar to the individual monomers. Simulations for the TEMPO-TEMPO dimer on graphite are shown in Figure , involving calculations in multiple locations with different positions and orientations. This shows that the upright configuration is the most stable, with a film thickness (i.e., the distance between HOPG and the highest atom of the TEMPO molecule) of 0.87 nm. In comparison, the tilted configuration is the third most stable configuration, resulting in a calculated film thickness of 0.65 nm.