Accurate adsorption energies for small molecules on oxide surfaces: CH4 /MgO(001) and C2 H6 /MgO(001).

A hybrid method is applied that combines second order Møller-Plesset perturbation theory (MP2) for cluster models with density functional theory for periodic (slab) models to obtain structures and energies for methane and ethane molecules adsorbed on the MgO(001) surface. Single point calculations are performed to estimate the effect of increasing the cluster size on the MP2 energies and to evaluate the difference between coupled cluster (CCSD(T)) and MP2 energies. The final estimates of the adsorption energies are 12.9 ± 1.3 and 18.9 ± 1.8 kJ/mol for CH4 and C2 H6 , respectively.