Theoretical Studies On The Structure, Chemical Bonding And Reactivity Of Several Transition Metal Oxide Clusters

Due to the specific physical and chemical properties, transition metal oxides (TMOs) have extensive technical applications in chemistry, biology, optics, materials and catalysis. The reactions on the surface of bulk are complex and not propitious for further research. Clusters exhibit unique physical and chemical properties because the size of clusters is between atoms and macroscopic systems. A well-defined cluster model will provide an effective method to study catalytic process at the molecule level. Since the last few decades, TMO clusters are becoming interesting in the field of theoretical as well as experimental. In this thesis, we report the theoretical studies which focus on several transition metal oxide clusters. A summary of our work is given as following:1. Starting from the Ni2O-/0 cluster, the electronic properties, structural evolution and chemical bonding of nickel oxide clusters are investigated by adding O content until the formula of M2O4. Density functional theory (DFT) calculations are performed to search for the lowest energy structures as well as low-lying isomers for both the anionic and neutral clusters. Generalized Koopmans’theorem is applied to predict the vertical detachment energies and simulate the photoelectron spectra (PES) of the most stable anions. Oxygen radicals are observed in the series of clusters and their existence shows the capability as catalyst.2. DFT calculations are performed to search for the lowest energy structures of the Cu4On-/0(n= 1-5). According to our calculations, the Cu40n-/0(n=1-5) clusters prefer to planar structures. The Cu4O4- cluster is a higher symmetrical structure with D4h symmetry and a peroxide unit is observed in the Cu4O5/0 clusters, suggesting that copper oxides can be used as an oxygen carrier.3. Extensive density functional (DFT) and ab initio [CCSD(T)] calculations are combined to investigate the lowest energy structures for Hf2On-/0 (n=1-6) clusters. Molecular orbital analyses are performed to elucidate the chemical bonding and the electronic and structural evolution in Hf2On-(n= 1-4) clusters. Spin density analyses reveal oxygen radical, diradical, and superoxide characters in the oxygen-rich clusters, except for the Hf2O5 cluster. We show that Hf2O3 contains a localized Hf2+ site, which can readily react with O2 to form the Hf2O5 cluster and may be considered as the molecular models for oxygen-deficient defect sites in hafnium oxides.