Theoretical Study Of The Structure And Properties Of Carbon Embedded Gallium Clusters

Clusters are relatively stable microscopic or sub-microscopic aggregates of several or even thousands of atoms,molecules or ions that are physically or chemically bound together and whose physical and chemical properties vary with the number of atoms they contain.In the development of cluster science,some specific clusters have atom-like characteristics,such as atomic orbital shape,valence electron shell arrangement（1S 1P1D 1F 2P...）.Chemical valence states,etc.,are called superatoms.Al₁₃^- and Al₁₂C have 40 valence electrons and perfect cage structure,which are representatives of magic number clusters.Ga and Al belong to the same group but their bonding properties are quite different.This paper determines the lowest energy isomers of Ga₁₂C using evolutionary method combined with density functional theories.Calculations show that Ga₁₂C with I_h symmetry are similar to the Al₁₃^- and Al₁₂C clusters.Isomers with C₂ symmetry can be considered to be distorted from D_5h symmetry(the lowest energy structure of Ga₁₃^-),but for 13 clusters,isomers with C_3h symmetry have never been determined.Their vibration spectra and density of states are presented,which will help to determine the ground state structure experimentally.Different structures suggest different bonding natures.The electronic structures of the low energy isomers are analyzed,and the charge populations and COHP values are calculated.The different structures of the Ga₁₂C cluster are determined by the competition between the ionic and covalent bonding and competition between the bond numbers and bond strengths.In chapter 4,low energy isomers of Ga₇C^-clusters are identified.The structure of Ga₇C^-cluster isomers is similar and can be regarded as a cage structure composed of gallium atoms composed of four pyramid and three prism combination,with carbon atoms embedded in the cage structure.We give the infrared spectra and Raman spectra of these isomers,which will help to determine the ground state structure experimentally.We analyzed the electronic structure of the low energy isomers and determined that the Ga₇C^-26 valence electron cluster is a strong magic number cluster forming a closed shell of1S²1P⁶2S²1D¹⁰2P⁶,which has outstanding thermal and chemical stability.By calculating the charge number and COHP value,the special structural properties of Ga₇C^-cluster isomers are affected by ionic bond,covalent bond,bond number and bond strength;Meanwhile,we compare the results with the analysis of bonding properties in Chapter 3,and the quantitative analysis of bonding interactions based on COHP shows that the covalent interactions of gallium clusters are significantly stronger than those of aluminum clusters.The electronic structure of gallium clusters generally conforms to the jellium model and exhibits metal bonding properties,but Ga-Ga interactions also exhibit weak covalent bonding characteristics.Saturation and orientation are intrinsic properties of covalent bonding,and covalent interactions affect the geometry of gallium clusters.