Group IVB transition metal oxides have numerous technological applications.For example,TiO2 is a typical photocatalyst,ZrO2 is used as solid-oxide fuel cells and so on.Moreover,ZrO2 and HfO2 can be considered as the leading candidates for the next generation high-gate insulator to replace SiO2 in field effect transistors due to their high dielectric constant.Gas-phase oxide clusters serve as well-defined molecular models which can provide detail information of metal oxide surfaces and defect sites.The current work focuses on the structural and electronic properties of tri-nuclear zirconium oxide clusters Zr3Ox/0(x=1 6).The selected optimized structures for stoichiometric clusters Zr3O6/0 are shown in Figure 1.The ground state for Zr3O6 anion is Cs(2A)(Figure 1a),which is based on a six-membered Zr3O3 ring motif with one capped and two terminal O atoms.Other structures are at least 0.5 eV higher in energy.For the neutral moiety,the singlet structure Cs(1A)(Figure 1b)is the lowest energy structure of Zr3O6,which shows similarity with the anionic ground state in geometry.The other chain-shaped structure C2(1A)(Figure 1c)is located to be 0.29 eV above the ground state.The first vertical detachment energy(VDE)for the anionic ground state is calculated to be 2.89 eV using generalized Koopmans theorem.Molecular orbital analyses are performed to elucidate the chemical bonding and structural evolution in these oxide clusters.