Phase diagram of subphtalocyanine ordering on Ag(111).

A model of subphtalocyanine molecules ordering on Ag(111) is proposed. We have demonstrated that the driving force of the ordering into honeycomb and hexagonal close packed patterns is a balance of intermolecular and subphtalocyanine-Ag interactions which can be generally expressed by a potential with infinite exclusion in a sufficiently large number of nearest coordination spheres of Ag(111) lattice and oscillatingly decaying behavior outside the sphere of exclusion. To cope with computational problems due to large size of the molecules compared to the substrate lattice period, we introduce the rescaling of Ag(111) lattice, and took into account an infinite exclusion of first, second, and third neighbors, attraction-of fourth and fifth, and repulsion-of sixth and seventh. The phase diagram is obtained by the lattice gas model using Monte Carlo simulations. Very strong first order phase transitions, causing the two-phase coexistence, were found between disordered and honeycomb as well as between disordered and hexagonal closed packed phases.