Computer simulations of the Adsorption of Xenon onto a C$_{60}$ monolayer on Ag (111)

We performed Grand Canonical Monte Carlo simulations to study the adsorption of Xenon on a substrate composed of C$_{60 }$molecules placed on top of a Ag(111) surface. The C$_{60}$ molecules form a commensurate structure at a distance of 0.227 nm above the Ag surface. The interaction potential between the Xe atoms and the substrate has two contributions: from the C$_{60}$ molecules and from the Ag atoms. In the simulations, the interaction with the Ag surface was computed using an \textit{ab initio} van der Waals potential, varying as 1/d$^{3}$. The interaction between the Xe atoms and each C$_{60}$ molecule was computed using a potential previously developed by Hernandez et.al. (E. S. Hernandez, M. W. Cole and M. Boninsegni, ``\textit{Wetting of spherical surfaces by quantum fluids}'', J. Low Temp. Phys. 134, 309-314 (2004)), who integrated the Lennard Jones interaction over the surface of a spherical buckyball. The total potential has especially attractive 3-fold sites, positioned~ 0.4 nm above the point between each three buckyballs. ~The low coverage uptake populates those sites, and then continues forming a monolayer. The adsorption isotherms show several steps, typical of substrates that have distinct adsorption sites. We compare the results with the experimental data. ~