Structure and electronic properties of Pdn clusters and their interactions with single S atom studied by density-functional theory

The geometries, stabilities and electronic properties of Pdn and Pdn−1S (n = 2-10) clusters have been systematically investigated by making use of density-functional theory (DFT) and all-electron spin-polarized generalized gradient approximation (GGA). The optimized geometries of the Pdn and Pdn−1S clusters have been considered, and the growth patterns of the Pdn−1S clusters have been discussed with respect to S-capped or S-substituted Pdn clusters. On the basis of the optimized geometries, various energetic properties including the average binding energies, the gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), the fragmentation energies, and the second-order difference of energies (▵2E) have been calculated for the most stable isomers of Pdn and Pdn−1S clusters. The investigation on the atomic average binding energies, fragmentation energies, and second-order difference of energies shows that the Pdn−1S (n = 4, 6, 8) clusters have high stability. Moreover, narrowing of the HOMO-LUMO gaps is usually found for the Pdn−1S clusters (except for the two with n = 3 and 9) as compared with the Pdn clusters, indicating that S atom doping leads to increase in the chemical activity of the Pdn clusters, which could be attributed to the transfer of charge from Pd atoms to S atom as evidenced by Mulliken charge population analysis.