Adsorption of triangular-shaped molecules with directional nearest-neighbor interactions on a triangular lattice

Using Monte Carlo and transfer-matrix methods the lattice gas model of adsorption of triangular-shaped molecules on a triangular lattice is studied. The constructed model takes into account the directionality of pairwise nearest-neighbor interactions between the adsorbed molecules. It is shown that a predominant character of "tip-to-tip" attractive interactions w 1 always leads to the formation of the honeycomb structure in the adsorption monolayer with local density ρ = 0.66(6). While, the values of "side-to-side" w 2 and "tip-to-side" w 3 interactions define the structure of close-packed phase. Depending on the values of the interactions the close-packed phase may have: (a) completely disordered structure; (b) frustrated honeycomb structure which is formed by Langmuir like adsorption onto 2D pores of the honeycomb structure; (c) ordered close-packed structure consisted of the molecules which all have the same orientation relative to each other and relative to the surface.