The Use of the Cluster Model for the Calculation of Chemisorption Energetics
Cluster size convergency of chemisorption energies is discussed with particular emphasis on recent results for adsorbates other than the hydrogen atom. For the hydrogen atom bond-preparing the cluster with one singly occupied orbital of the same symmetry as the hydrogen 1s orbital leads to a rather quick convergence of the chemisorption energy. Bond-preparation can in this case be simply interpreted in terms of the formation of a covalent bond between two radicals. The results obtained for adsorbates like fluorine and oxygen suggest a different interpretation of bond-preparation. A picture where the adsorbate electrons should fit into the electronic structure of the cluster is more general and can be applied for all these adsorbates. Finally, some preliminary results for CO chemisorption on small copper clusters are discussed and compared to recent cluster experiments. It appears that cluster size convergency in this case is faster if the cluster geometry is optimized than if the cluster geometry is fixed to model a particular surface.
KeywordsCluster Size Lone Pair Bonding Mechanism Occupied Orbital Copper Cluster
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