Density-Functional Investigations On Small M_nC~±(M: Fe, Co, Ni, Cu; N=1-5) Clusters

Atomic or molecular cluster has attracted great interest due to its many unique properties different from the single atom (molecule) as well as the bulk materials and its potential applications in science and technology. Since the discovery of metallocarbohedrenes (Met-Cars), the mixed clusters which consist of transition metal and carbon have attracted extensive attention, especially the study of the catalytic growth of the Single-Walled Carbon NanoTubes (SWCNTs) has become the focus of research.In the first chapter, we tried to give a brief introduction to the properties and the recent research status of clusters, transition metal clusters, SWCNTs and mixed clusters composed of transition metal and carbon.In the second chapter, the development of Density-Functional Theory (DFT), the computation methods adopted in cluster science and the PWscf software used in the present work have been described in detail.In the third section, Density-Functional Theory investigation results concerned about the small charged clusters MnC±(M: Fe, Co, Ni, Cu; n=1-5) have been presented. The results contain some important parameters such as the ground-state geometrical structures, electronic structures and magnetic properties of MnC±clusters. It is found that the addition of one electron to neutral MnC has less influence on the ground-state geometrical structure while the subtraction results in big change. According to the analysis of the second order energy difference and the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of MnC±, Cu3C- possesses relatively higher stability among all those strucutres of MnC±. The adiabatic ionization potential and the adiabatic electron affinity of MnC are also calculated. Both the adiabatic ionization potential and electron affinity of MnC decrease as increasing the cluster size. The interactions between TMn (TM: Fe, Co, Ni,) and C±are closer and are all apparently stronger than that of Cun and C±,and the interaction strengths are all enhanced for the positively charged clusters, which may led to a better environment for growing the single-walled carbon nanotubes according to the interaction strength model.