First Principles Study On The Structure And Properties Of MBe_n (M=Fe,Co,Ni) (n=2-12) Clusters

In this thesis, we investigate the geometric, electronic and optical properties of MBen(M=Fe,Co,Ni) clusters using density functional theory (DFT). The main contents are presented as the followings: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, we introduce the basic properties of clusters. Then, some commonmethods in experimental and theoretical studies on clusters are discussed, including the preparation and detection of clusters, and theoretical studies. Then, research on clusters is reviewed and previewed. At last, we simply describe the purpose and results of our work on clusters.In Chapter 2, we introduce the basic concept and progress of DFT. 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 exchange-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, we investigate the geometric, electronic properties of MBen(M= Fe,Co,Ni) . The results show that the doped atoms are capped on host clusters and surrounded by Be atoms. The investigated magnetic moments confirm that the Co atomic magnetic moments of CoBen (n=1-12) clusters display an oscillation features. In addition, the Co atomic magnetic moments of CoBe6 is the smallest among all clusters, due to strong hybridization between the 4s, 3d state of Co and 2s, 2p state of Be and short Co-Be average bond distance and low symmetry. It is found that CoBe5 and CoBe10 clusters are more stable than neighboring ones. The geometric structures of NiBen clusters are influenced by spin multiplicities. The magnetic moment of the Ni atom in NiBen clusters is quenching around n≥4, due to strong hybridization between the 4s and 3d states of Ni and the 2s and 2p states of Be. It is concluded that impurity increases the stabilities and the chemical activation of Be cluster. It is found that NiBe4 and NiBe10 clusters are more stable than neighboring ones. The magnetic moment of the Fe atom of FeBen (n=5,7,12) are quenching due to strong hybridization between the 4s, 3d state of Fe and 2s, 2p state of Be and short Fe–Be average bond distance and low symmetry.By contrast to Ben cluster, it is concluded that impurity increases the stabilities of Be cluster. The magic of MBen(M=Fe,Co,Ni) is explained by geometric model, by analyzing the properties of electrons and geometric structure.