Quantum chemical study of small palladium clusters

The extended Huckel method with an electrostatic two-body correction has 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 those of bulk palladium, was found to be the preferential direction for cluster growth in the absence of external field. In accordance with the experimental results, these close-packed particles show a significant split in the valence d-zone. The energetic gap between HOMO and LUMO narrows from 3.217 to 0.68 eV as the cluster grows from two to 13 atoms. The LUMO has a bonding character toward Pd-Pd bonds, whereas HOMO is antibonding, so one can suggest that both donating and accepting interactions are favorable for strengthening of clusters, Occupation of 5s and 5p orbitals increases during cluster growth, while the net charge on the outer atoms remains very small. The results obtained for two to six atomic clusters are in good agreement with first principle calculations. Very close similarity with Rh cluster growth was observed. (C) 1998 Elsevier Science B.V. All rights reserved.