First-principles calculations of small PdnAlm (n+m≤6) clusters

The equilibrium geometries, stabilities and electronic properties of small PdnAlm (n+m≤6) clusters have been systematically investigated by density functional approach. The optimized geometries exhibit that the lowest-energy structures of PdnAlm clusters prefer a three-dimensional configuration, except for Pd2Al2, which prefers a two-dimensional structure. The binding energy (Eb), HOMO-LUMO energy gaps (Eg), vertical ionization potential (VIP), and vertical electron affinity (VEA) were calculated and discussed. The obtained results show that the bimetallic clusters are more stable than the monometallic clusters, indicating that the doping of Al atoms enhances the stability of pure Pdn clusters. Further, a closer inspection of the results showed that the stability of these clusters is directly related to the number of Pd-Al bonds in the cluster. It increases with increasing of the number of Pd-Al bonds. The calculated HOMO-LUMO energy gaps of PdnAlm clusters are in the range of 1.55-2.94 eV, indicating that these clusters are of semiconducting feature. The VIP varies from 5.94 to 7.06 eV, and the VEA ranges from 0.84 to 1.98 eV. Thus, the values of VIP are much higher than the VEA values, implying that the bimetallic clusters easily accept electrons.