All the simulations showed some degree of molecular aggregation: the molecules form nanoislands possessing a hexagonal structure with a mean distance between their center of mass of 14.2 Å. At low coverages (i.e. N 2 = 2 2 and 3 2 ) free molecules diffuse and aggregate to form a single cluster. At higher coverages (i.e. 4 2 ), all molecules form first small clusters in few ps, that subsequently migrate and merge. Aggregates larger than about 10 molecules hardly diffuse on the surface, and at the highest coverages (i.e. 5 2 , 6 2 and 7 2 ), the density of molecules is so high that the aggregation occurs after the very few picoseconds from the beginning of the simulation. We also calculated the stabilization energy per molecule in the cluster using the following expression: