As can be seen in Figure , for low temperatures and high pressures more tightly packed structures form. This favors the standing polymorphs. With increasing temperature, packing density becomes less important relative to bonding to the surface, which yields a transition from standing to lying polymorphs. Finally, for even higher temperatures and lower pressures, the molecules desorb. In passing, we note that the qualitative agreement with the phase diagram from Egger et al. is excellent, despite small quantitative differences due to the different methodologies.