The Geometry Prediction And Properties Analysis Of Boron-based Clusters

B is an element in IIIA, its electronic configuration is1s2s22p1, and it is electron deficiency. In recent decades, the chemical bonding of boron has attracted much attention, and lots of experimental and theoretical studies of the boron and boron-based clusters have been reported.In this thesis, the geometric structures of (B2O3)n (n=1-6) clusters has been optimized and its properties has been analyzed at first; secondly, we design the planar structures X@BnHn (X=Be,B+,V’,Cr,Mn+; n=5-8), and investigate their properties and bonding style.The main works are listed as follows:1. First Principle Structural Determination of (B2O3)n (n=1-6) Clusters:from Planar to CageThe structure of (B2O3)n clusters (n=1-6) are investigated using the method combining the genetic algorithm with density functional theory. Benchmark calculations indicate that TPSSh functional is reliable in predicting the energetic sequences of different isomers of (B2O3)n cluster compared to the high-level coupled cluster method. The global minimum (GM) structures of (B2O3)n clusters are planar up to n=3, and cages at n=4-6. A Td fullerene is found in the GM structure at n=6. The stability of three dimensional structures increases with the size of the cluster according to the analysis of the calculated atomization energy. Natural bonding analysis given by adaptive natural density partitioning reveals delocalized π-bonding in the4-membered and6-membered rings, and it is aromatic at the centers of cages and rings.2. Density Functional Investigation of X@BnHn (X=B+, Be; n=5-8)The stability of X@BnHn (X=B+, Be; n=5-8) is investigated by density functional theory. Geometry optimization shows that both the radius of the center atom and the ring size make contribution to the stability of X@BnHn structure. All the optimized structures are thermodynamics stable according to the large HOMO-LUMO gap, bonding energy, vertical ionization potential and vertical electron affinity. Nuclear independent chemical shift reveals that the (quasi-)planar structures are π aromatic, which is confirmed by chemical bonding analysis. 3. Benzene Analogues of (quasi-)planar M@BnHn Compounds (M=V-, Cr, Mn+):A theoretical InvestigationThe stability of M@BnHn (M=V-, Cr, Mn+; n=5-8) is investigated by density functional theory. For n=6-8, the isomers possess (quasi-)planar local minima showed by geometry optimization at TPSSh/6-311+G**level. All the optimized structures are thermodynamics stable according to the large HOMO-LUMO gap, binding energy, vertical ionization potential and vertical electron affinity analysis. The peripheral and central atomic radius fit each other best at n=7confirmed by the variation of the binding energy values. The availability of d atom orbitals in M for participation in the π-delocalized bonding with the peripheral ring leads to the aromaticity of the (quasi-)planar structures, and makes them the benzene analogues. This work establishes firmly the metal-doped borane rings as a new type of aromatic molecule.