The molecular geometric and electronic structures of ligand-stabilized binary transition-metal cluster [PdAu₈(PR₃)₈]^2＋ (R＝Me, OMe, H, F, Cl, CN) have been investigated by means of ab initio MP2 and density functional theory (DFT) methods. The bonding energies of Pd-Au₈(PR₃) and [PdAu₈]^2＋-PR₃ have been also analyzed on the basis of calculations. The MP2 and local density functional SVWN methods have good performance in reproducing the experimental geometric features. The non-local exchange- correlation functionals, such as BP86, PBE and BLYP, and hybrid functional B3LYP tend to overestimate the Pd-Au and Au-Au bond lengths. The studies of the electronic structures show that the metal cluster core [PdAu₈]^2＋ was formed by the d-d electron interaction of Pd and Au atoms. The bonding of [PdAu₈]^2＋-PR₃ complexes can be described as a synergistic combination of σ-donor and π-acceptor interactions between [PdAu₈]^2＋ and PR₃ ligands. Adding the PR₃ ligands led to the increases of the bonding interaction of Pd-Au and the HOMO-LUMO gap and, therefore, also the increase in the stability of the cluster. It was found that the effect of the electron donating or withdrawing ability of PR₃ groups on the geometries of [PdAu₈(PR₃)₈]^2＋ was small, but that on the bonding energies of [PdAu₈]^2＋-PR₃ was large. The energy decomposition analysis results show that the orbital interaction energies of the [PdAu₈]^2＋-PR₃ bonding are very close to each other, so the magnitude of the non-orbital interaction energy plays a crucial role in the stabilization of [PdAu₈(PR₃)₈]^2＋ complexes.

Key words: transition-metal cluster, ab initio, density functional theory, electronic structure, energy decomposition analysis