QUANTUM-CHEMICAL STUDY OF SMALL PALLADIUM CLUSTERS

The extended Huckel method with an electrostatic two-body correction h as been used to find the structure of small Pd-n clusters For n=2-13. Twins formation. with metal-metal bond lengths slightly smaller than t hose of bulk palladium, was found to be the preferential direction for cluster growth in the absence of external field. In accordance with t he experimental results, these close-packed particles show a significa nt split in the valence d-zone. The energetic gap between HOMO and LUM O narrows from 3.217 to 0.68 eV as the cluster grows from two to 13 at oms. The LUMO has a bonding character toward Pd-Pd bonds, whereas HOMO is antibonding, so one can suggest that both donating and accepting i nteractions are favorable for strengthening of clusters, Occupation of 5s and 5p orbitals increases during cluster growth, while the net cha rge on the outer atoms remains very small. The results obtained for tw o to six atomic clusters are in good agreement with first principle ca lculations. Very close similarity with Rh cluster growth was observed. (C) 1998 Elsevier Science B.V. All rights reserved.