Geometrical frustration of an argon monolayer adsorbed on the MgO (100) surface: An accurate periodic ab initio study

We present an accurate first-principles method for calculating the energy of physisorption, based on a fully periodic local Moller-Plesset second order perturbation theory (LMP2) treatment. The LMP2 inter-surface-adsorbate interaction energy is scaled with a factor, obtained by comparing the method error of LMP2 versus coupled cluster singles doubles theory with perturbative triples at the basis set limit in small clusters mimicking the system under study. This method is applied to the investigation of geometrical frustration in argon monolayers adsorbed on the MgO (100) surface. It is found that several arrangements of the argon monolayer, i.e., 3 x 2, 4 x 2, optimal hexagonal, and zeta x 2 1D noncommensurate have very similar adsorption energies, which agrees with the experimental observations. Moreover, this study provides further insight in to the Ar-MgO adsorption process and sheds light on a controversy among different experiments. The calculated adsorption energy of 2.3 kcal/mol is in a very good agreement with the experimental values, which range from 2.0 to 2.3 kcal/mol, and provides a new benchmark for this system.