Theoretical Study Of Li-doped Be_N And Ni-doped B_N Clusters

The dissertation is devoted to the study of formation and characterization of Li-doped BeN(N=2-15) and Ni-doped BN(N≤6) clusters. Clusters are aggregates of atoms or molecules ranging in size from two to tens of thousands of monomer units. Recently, cluster science has undergone an explosive growth in activity. The carbon is the chemical element which the humanity most early knew, along with the discovery of C₆₀ and so on carbon clusters, enable the people also to have the new understanding to the carbon, and therefore opened a broad-new research area. Since the 1990s, the scientists which have invested the C₆₀ research are so many, involves discipline is broad, the publication paper numbers are so many, in the scientific history is rare. But each kind of new cluster of discovery, can start a wave of the research upsurge. Actually, C₆₀ and so on fuller alkene also is only a carbon cluster of one kind, other structural styles clusters, other elements clusters, as well as richer multi- element clusters, all is possible to become the new research hot spot.The researchers are interested in the clusters regards beryllium, lithium, boron, nickel and so on element, because unusual structure will lead to fascinating properties, even to a potential for industrial application through extensive investigation. The study of the properties is often attractive from both the fundamental and the aesthetical points of view. Spectroscopic investigation of the clusters combined with theoretical study has become an active field of research in the last decades. Hand in hand with the advances in experimental studies, there has been much progress in efforts to derive theoretical models for larger clusters of beryllium, lithium, boron, nickel and so on element. The combined efforts of experimentalists and theoreticians have led to a detailed physical insight into the microscopic interactions that govern the structural and dynamic behavior of these clusters. In this thesis, we investigate the structures and properties of Li-doped BeN(N=2-15) and Ni-doped BN(N≤6) clusters using frst-principles quantum chemistry methods based on density functional theory (DFT). Main results and conclusion could be summarized in the following:1. Density functional calculations have been carried out for Li-doped BeN (N=2-15) clusters at the B3LYP/6-31G(d) level. Geometry of various isomeric structures of the clusters were optimized and their energies were compared to find the most stable isomers. Based on the analysis of the theoretical results, the equilibrium geometries, vibrational frequencies, relative stability, the electronic properties and polarizabilities are discussed. The resulting geometries show that Li prefers to be on the periphery of Be clusters. The results indicate that size n=4,9 and 13 are magic numbers of the BenLi clusters. Along with the size increase, the gap gradually reduce, the s, p orbits hybridization gradually strengthens. Our calculations demonstrate that Li impurity decreases the binding energy per atom while increases the polarizabilities of BeN clusters. 2. The full geometry optimization and the magnetic property computation to the small clusters BnNi(n≤5) were performed using generalized gradient approximate (GGA) method based on the density functional theory, the Becke exchange gradient revision and the Perdew-Wang connection gradient revision were chosen, and the double numerical basis including p-polarization function (DNP) were used, and had determined their lowest energy structures. The computed results indicated that the spinning multiplicities of the lowest energy structures for small clusters BnNi(n≤5) respectively are 2, 1, 2,1, 2; After Ni-doped into the BN clusters to increase their average binding energy; The Ni atomic magnetic moment and total magnetic moment of clusters showing the oscillation tendency as increasing of clusters size.