Spin and structural features of oxygen dissociation on tetrahedral Ag20 and Ag19Au clusters

Abstract

The spin-crossing mechanism of oxygen dissociation on Ag₂₀ and monodoped Ag₁₉Au clusters was investigated via spin-polarized scalar-relativistic DFT calculations using the PBE, TPSSh, M06L, mPBE, BLYP, OLYP, and B3LYP functionals. In particular, the singlet and triplet O–O bond rupture pathways at vertex-edge and facet-edge sites on the tetrahedral clusters were studied. The calculations reveal that for the Ag₂₀O₂ and Ag₁₉AuO₂ complexes, the spin inversion from the triplet to singlet state occurs during the last step, which involves O–O bond rupture through a singlet transition state (TS). When spin crossing during oxygen dissociation on the clusters is considered, the activation energies decrease by 10–29 kJ mol⁻¹; however, they are still high due to the magic nature of the clusters and high vertical spin excitation energies. For these silver clusters, size effects based on the relationship between the TS structure and oxidation activation energy were predicted.