CO adsorption on CeO2(111): A CCSD(T) benchmark study using an embedded-cluster model.

A benchmark model that combines an embedded-cluster approach for ionic surfaces with wavefunction-based methods to predict the vibrational frequencies of molecules adsorbed on surfaces is presented. As a representative case, the adsorption of CO on the lowest index non-polar and most stable facet of CeO 2 , that is, (111) was studied. The CO harmonic vibrational frequencies were not scaled semiempirically but explicitly corrected for anharmonic effects, which amount to about 25 cm − 1 with all tested methods. The second-order Møller–Plesset perturbation method (MP2) tends to underestimate the CO harmonic frequency by about 40–45 cm − 1 in comparison with the results obtained with the coupled-cluster singles and doubles with perturbational treatment of triple excitation method [CCSD(T)] and independently from the basis set used. The best estimate for the CO vibrational frequency (low-coverage case) differs by 12 cm − 1 with the experimental value obtained by infrared reflexion absorption spectroscopy of 1 monolayer CO adsorbed on the oxidized CeO 2 (111) surface. In addition, a conservative estimate of the adsorption energy of about −0.22 ± −0.07 eV obtained at the CCSD(T) level confirms the physisorption character of the adsorption of CO on the CeO 2 (111) surface. [ABSTRACT FROM AUTHOR]