Adsorption of CO molecules on a MgO(001) surface. Model cluster density functional study employing a gradient-corrected potential

A density functional model cluster study of CO adsorbed on a MgO(001) surface has been carried out in order to accurately estimate bonding and vibrational parameters of the adsorption complex and to make a thorough analysis of the observables. Computed data for extended stoichiometric cluster models of varying size were obtained by employing a gradient-corrected exchange-correlation energy functional and by correcting for the basis set superposition error. The surface Madelung field was represented by embedding the MgO cluster models in an array of point charges; their value, lower than the nominal ionic one, ±2 au, was derived from density functional model slab calculations of an MgO surface. The specified approach brings calculated observables, in particular the adsorption energy, in closer agreement with experiment as compared to previous studies at the local density functional level of theory. A constrained space orbital variation analysis reveals that σ donation from CO to MgO forms, along with the electrostatic attraction, a significant component of the adsorption interaction. A small stabilizing effect of the π back donation from the neighboring oxygen ions to CO has also been found.