Density Functional Theory Calculations Of Boron And Li,Al Atoms Doped Boron Clusters

In this thesis, we investigate the geometric and electronic properties of boron, lithium doped boron, aluminum doped boron clusters using density functional theory(DFT). The main contents are presented as the following:In chapter 1, we give a brief introduction to clusters. With a size between those of atoms and macroscopical systems, clusters have many unique properties, and attract much experimental and theoretical research attentions. At first, some basic concepts, general properties of clusters have been briefly summered. Then, some common methods in experimental and theoretical studies on clusters are introduced, including the preparation and detection of clusters, and theoretical studies. At last, we have introduced the research background and meaning of boron and boron doped clusters.In chapter 2, the basic concepts and progress of DFT are introduced. Development of quantum chemistry promotes the establishment of DFT. Thomas-Fermi model is the first theory using density of electrons as the main variable. Theorem of Hohenberg-Kohn is the fundament of DFT and is developed to Kohn-Sham equation, which can be used to perform real calculations. Now, new corrections and extensions, together with developed exchang-correlation functionals, have made DFT more accurate and suitable for more systems. At the end of this chapter, we introduce the Gaussian and Dmol3 software.In chapter 3, the Bn (n=2-15) clusters with different growth pattern were calculated and analyzed. The results show that linear structures are unstable and strong metallicity. Planar and quasi-planar structures are most stable and weak metallicity. The stability and metallicity of tree-dimensional structures are ordinary comparing to the linear structures and planar or quasi-planar structures. B12 and B14 are magic number clusters.In chapter 4, the B and Li dual-doped clusters Bn-1Li(n=2-13),(BLi)m (m=1-6) are studied. The results show that: for Bn-1Li(n=2-13) clusters, Li is always at the periphery of the main clusters and combining with the main cluster via coordination number at least, some even absorbed above the main clusters. High concentration of doping (Li:B=1:2～Li:B=1:3) can improve the chemical activity and metallicity, but it can also reduce the stability of the clusters. B3Li and B5Li were the magic number clusters. For (BLi)m (m=1-6) clusters, m=5 can be seen as a transition point from two-dimensional to three-dimensional structure. B-Li bond lengths longer than B-B bond lengths. Charges transferred from Li atoms to B atoms. The clusters have high chemical activation. B4Li4 is magic number cluster.In chapter 5, the (AlB₂)_m (m=1-6) are studied, the results show that: for (AlB₂)_m (m=1-6) clusters, the (AlB₂)₅ cluster is metallic. B-Al bond lengths longer than B-B bond lengths. Charges transferred from Al atoms to B atoms. The 2p sub-shell of B atoms in (AlB2)m does behave as a core orbital and take an active role in the bonding, which make the clusters easier to form delocalizedÏ€-bond. The clusters display semimetal features, and have high chemical activation.In the last chapter, summarizations of all the works are given.