CHEMISORPTION THEORY OF AMMONIA ON COPPER

We present local-density-approximation calculations of ammonia adsorption on copper clusters of different sizes (6 to 18 atoms) modelling the (100) and (111) surface. Including for some of the copper atoms only one instead of eleven electrons explicitly in the calculation, did not always work satisfactorily. Comparison of adsorption energies for clusters of related geometry indicates a preference for onefold adsorption. This is due to the Pauli repulsion of the lone-pair orbital of ammonia with the copper 3d electrons. which is minimal for onefold adsorption. as well as an interaction with 4s electrons, which is most attractive in the onefold geometry.