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 LC AO-LDF molecular-cluster approach. A realistic description of the elec tronic structure of the Lewis acid site has been found to be the most important point of the chemisorption simulation. An excellent agreemen t between experiment and theory has been obtained by considering the d angling bonds of ZnO(0001) to be empty. The bonding of CO to the surfa ce is dominated by a covalent interaction involving a donation from th e 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 electrostat ic interaction between the NH3 dipole moment and the Lewis acid site i s at least as important as the covalent one.