Chemically Accurate Adsorption Energies: CO and H₂O on the MgO(001) Surface

Hybrid MP2:DFT-D structure optimizations are performed at BSSE-free CBS-extrapolated potential energy surfaces for molecule-oxide surface interactions (BSSE, basis set superposition error; CBS, complete basis set limit). Subsequently single point MP2 calculations are performed to estimate the effects of increasing the basis set size in the CBS extrapolation and increasing the cluster model size. The resulting estimates of the periodic MP2 limit agree within 1 kJ/mol with Local MP2 calculations using periodic boundary conditions. Single point CCSD(T) calculations are performed to determine ΔCC = CCSD(T) - MP2 energy differences. The final hybrid MP2:DFT-D+ΔCC estimate for CO on the MgO(001) surface at low coverage, -21.2 ± 0.5 kJ/mol, is in close agreement with the reference energy derived from temperature-programmed desorption experiments, -20.6 ± 2.4 kJ/mol. For H₂O on MgO(001), at limiting zero coverage, we predict an adsorption energy of -53.7 ± 4.2 kJ/mol which falls in the range of values, -55.8 ± 12.2 kJ/mol, derived from a high coverage low energy electron diffraction experiments and estimated lateral interactions.