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 a nd vibrational parameters of the adsorption complex and to make a thor ough analysis of the observables. Computed data for extended stoichiom etric cluster models of varying size were obtained by employing a grad ient-corrected exchange-correlation energy functional and by correctin g for the basis set superposition error. The surface Madelung field wa s 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 surf ace. The specified approach brings calculated observables, in particul ar the adsorption energy, in closer agreement with experiment as compa red to previous studies at the local density functional level of theor y. A constrained space orbital variation analysis reveals that a donat ion from CO to MgO forms, along with the electrostatic attraction, a s ignificant component of the adsorption interaction. A small stabilizin g effect of the pi back donation from the neighboring oxygen ions to C O has also been found.