We have studied the adsorption of H-2 and CO molecules, as well as the dissociation of H-2, on the (ZnO)(6) cluster model using the ab initio Hartree-Fock method. The effective core potential was used for Zn, C, and O atoms at double-zeta-type valence basis set level, whereas for H we used Dunning's basis set, We have also added polarization and diffuse functions to the O, C, and H basis set. The CO molecule interacts with the lowest coordination zinc sites which are located on the edge between the (0001) and (10 (1) over bar 0) surfaces. The decrease in CO bond length upon adsorption on ZnO surfaces is associated with the charge transfer from CO to the surface, Our calculations indicate the 5 sigma orbital from adsorbed CO stabilized to a 1.56 eV deeper energy, Of all the configurations investigated, the molecular H-2 interaction has the lowest binding energy with a decrease in H-2 bond strength, The H-2 molecule also dissociates on the zinc and oxygen sites of the ZnO cluster, and the preferential dissociation site is the oxygen which has a coordination number of two. The H-2 dissociation shows a large stabilization energy for the most stable adsorption site which is the lowest coordination site. Molecular CO and H-2 adsorption yields a smaller change in the estimated energy gaps and ionization potentials, We have also analysed the geometry of the adsorbed molecules, the Mulliken charge, the orbital SCF energies, and also the molecular orbital densities and contour plots. Our results are compared with the available experimental data, (C) 1997 Elsevier Science B.V.
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