A LCAO-LDF STUDY OF CO AND NH3 CHEMISORPTION ON ZNO(0001)

The coordination of CO and NH3 to ZnO(0001) has been studied by the LCAO-LDF molecular-cluster approach. A realistic description of the electronic structure of the Lewis acid site has been found to be the most important point of the chemisorption simulation. An excellent agreement between experiment and theory has been obtained by considering the dangling bonds of ZnO(0001) to be empty. The bonding of CO to the surface is dominated by a covalent interaction involving a donation from the CO HOMO into the empty AOs of the Zn surface ions. The same kind of mechanism is active for the NH3 chemisorption, even if the electrostatic interaction between the NH3 dipole moment and the Lewis acid site is at least as important as the covalent one.