Packing effects in mixed Lennard-Jones clusters and potential energy functions for alkylthiolates and C60 on the gold (111) surface

In the first half of this work, we examined high-symmetry global minimum (GM) energy structures of small argon-xenon Lennard-Jones clusters. We found columnar GM structures with 4- and 5-fold symmetry. The stability of these structures was most sensitive to packing effects due to the mixed-interaction equilibrium distance. We then found several GM structures containing four-membered Xe rings. The most notable GM structures found were for stoichiometries (Ar,Xe) of (7,8) and (5,13), with, respectively, octahedral and decahedral symmetries. Again, packing effects determined the structure of the GM. In the second half of the work, we fit simple potential energy functions for the interaction energy of thiolate sulfur and C60 with the Au (111) surface to theoretical data. Both fit potentials contain a Morse potential in z and an exponentially decaying corrugation potential. For thiolate S, the corrugation may be attractive or repulsive, but the fullerene potential required an always-repulsive corrugation