Theoretical Studies Of The Structure And Property As Well As Hydrogen Storage Performance Of Mg-doped Boron Clusters

The DFT method was used to study the possible configurations, stabilities as well as the electronic properties of Mg-doped boron clusters in this thesis. We studied the stable hydrogenated configurations of Bn and MgBn (n= 2～7) clusters, i.e. BnH2 and MgBnH2 clusters. After that, the physisorption and chemisorption behaviors of H2 on Bn and MgBn clusters was also investigated, including the dissociation mechanism of H2 on Bn and MgBn(n = 2～7) clusters. Furthermore, we designed a novel boron molecule with a structure similar to that of benzene. The 2D hydroboron sheets were obtained by extending that cyclic boron molecule. Finally we studied the adsorption and dissociation property of O2 on Al(111) covered by different amounts of O atoms. The diffusion behavior of O atom in the oxidized Al(111) surface have been investigated. This study includes the following four sections:1. The stablest structures as well as mestable structures of MgBn±m(n=1～7 and m=0, 1) have been investigated by UB3LYP/6-311+G* method, and during this investigation the effect of multiplicity was also considered.. The average binding energy, fragment energy as well as second-order difference energy were computed to discuss the structural stability of the above clusters; Also the adiabatic ionization potential (A.I.P) and adiabatic electron affinity (A.E.A) of neutral MgBn clusters and HOMO-LUMO gap energies of all the three kinds of Mg-doped boron clusters were calculated. At last, the NBO analysis was done to study the natural population of MgBn±m (n=1～7 and m=0,1).2. The stable configurations of BnH2 and MgBnH2{n= 2-7) clusters as well as their structure stabilities and electronic properties were studied by the method of B3LYP/6-311++G(d,p). The physisorption behaviors of H2 molecule on Bnand MgBn(n=2～ 7) clusters were calculated at wB97XD/6-311++G(d,p) level, including the calculations of adsorption heat as well as the stable adsorption sites. From two aspects of thermodynamic and dynamic, the dissociation properties of H2 on Bn and MgBn [n=2～7) clusters were explored, including the calculations of dissociation heat, Gibbs free energy change as well as barrier energy to investigate difficulty extent of H2 dissociation on the above clusters.3. We designed a cyclic borane (B6H12) molecule with a benzene-like structure, where the six B atoms are in the same plane. Three methods of B3LYP, MP2 and CCSD with 6-311++G** basis were used to investigate the structure, electronic property and stability of it. Then, our attention focused on three hydroboron derivatives with fused rings of B10H18, B14H24 and B16H26. The stabilities and electronic properties of these homologs were studied. Finally, we investigated three types of two-dimensional novel infinite hydroboron sheets with diborane as a building block. The results of the phonon spectra ensure the dynamic stabilities of these predicted structures. Furthermore, these three types of hydroboron sheets have different band gap energies of less than 3.0 eV. Some investigations on the optical properties have also been performed. The predicted sheets can be candidates of semiconductors, and the band gap energy can be tuned by the positions of the bridge4. In the castep mode, GGA/PBE method was used to study the stable configurations of Al (111) surface with four different coverages (0.25M,0.50M,0.75M, LOOM) of O atoms, including the calculations of average adsorption heat as well as the charge transference from Al atoms to O atoms. Moreover, the physisoprtion and chemisorption of O2 molecule with four different oxygen coverages on the Al(111) surfaces were investigated, including the calculations of adsorption heat and dissociation heat. The diffusion behaviors of single O atom with different oxygen coverages on Al(111) surfaces were probed, including the stable adsorption sites of O atom as well as the diffusion energy barriers.