Computational Studies For Excited States Of Small Atomic Clusters And Heterofullerenes

In the past decades, research on clusters has been one of the largest as well as themost rapidly developed branches of physics. Taking advantage of rapid progress in theexperimental technology, it is much readily to produce clusters with different size and tostudy their physical properties; on the other side, the development of computer andalgorithms make it possible that we can carry out first-principles calculations to obtainthe geometry and the electronic structure of the small clusters and to simulate thedynamics. Nowadays, in this branch, the focus issues are to study the geometry, bonding, and electronic structure properties, to observe how the properties change with incrementof its size, and to discover more novel physical and chemical properties. The calculationsabout clusters are the subjects of this dissertation.Transition metal carbide clusters (met-ears) have been a subject of intenseinvestigation in recent years due to their promising applications in materials sciences, microelectronies, nanotechnology, catalysis, solid state chemistry, and so on. And thestudy of fullerenes is one important part of nanotechnology. We can change the physicaland chemical properties of fullerenes to get the material that we need by doping. All ofthose arouse people's enthusiasm for the study of clusters.In this dissertation, using the density functional theory (DFT) we mainly investigatethe met—cars and heterofullerenes clusters. The dissertation is divided into the followingfour chapters.In Chapter 1, the actuality and development of cluster researching are introducedbriefly.In Chapter 2, the history and actuality of quantum chemistry computation are brieflyintroduced, and we mainly describe the density functional theory (DFT) as well as somepopular ab initio software packages, which are our theoretical foundations andcomputational implements to deal with cluster system.In Chapter 3, the works concentrate on the study of small clusters. In this part, density functional calculations are performed to study MC₂ (M=V, Cr, Fe and Co), MC₃(M=Sc, V and Cr), TiC₅ and SiN clusters in their neutral and anionic states. Theequilibrium geometries, electronic configurations and electron affinities of these clusters are obtained. Time-dependent DFT (TDDFT) is used to calculate the excited states. Atheoretical assignment for the features in the experimental photoelectron spectrum isgiven. Our results compare well with the available experimental results, and show thatTDDFT can give the convincing prediction for the excited state properties of clusters.In Chapter 4, the study on the structural and electronic properties of C₅₉B^- andC₅₉N⁺ is described. Though the C₅₉B^- and C₅₉N⁺ are isoelectronic analogues to C₆₀, it isfound that doping induces great changes in electronic properties. The doped atoms bringon impurity energy levels and make B in C₅₉B^- and N in C₅₉N⁺ act as a hole and anelectron donor respectively. The PDOSs (partial densities of states) indicate thehybridization between the orbitals of the doped atoms and of the carbon atoms of thecages.