| The atomic cluster is one of the elementary cell which forms nanometer body, membrane, multilevel membrane and nanometer structure, so the theoretical research for ground-state structures, energy level distribution and electronic properties of its is one of the important subject in the design of microstructure of new material, and has great signification in"custom-made"new material with specific performance. Even more focus has been put on binary small clusters including the IVA element, because of their fundamental interest and potential application in nanoelectronics. Along with the rapid developmentt of computational methods and computer technology, now it is possible to study the geometry, electronic structure and many other properties of small clusters from first-principles calculations, and get more and accurate information. In the thesis, we investigate the geometric, electronic properties and energy level distribution of small IVA–VII binary clusters using first-principles quantum chemistry methods based on ab initio theory and density functional theory (DFT). The main contents are presented as the followings:First, the geometrical structures, vibrational frequencies and dissociation energies of X2Cl (X=C,Si,Ge), Sn2X and Pb2X (X=Cl, Br, I) clusters are studied. The ground state of clusters are obtained. The results indicate that the C2Cl? has a linear structure at ground state,while other clusters take a bend shape. At all levels of calculation, As atomic number increase, the calculated bond length show an increasing trend, while the binding energy (De) show a decreasing trend. The electronic properties studied find that the charge always transfer from the IVA element to halogen atom, which show halogen atoms can be expected to work as the electron acceptor. The electron correlation effects is investigated at different theoretical level. It has strong influence on the geometries and stabilities of the present species; the effects shorten the bond length, reduce the bond angle, increase the vibrational frequencies and thus enhance the stability. Three forms of electron affinity (EA) are also calculated, which are evaluated as the difference of total energies. The results are in good agreement with theoretical results reported. As halogen atomic number increase, the EAs show an decreasing trend ,which reveal the stability difference of these clusters.SinCl and SinCl? (n=1–6) clusters are investigated systemically using density functional theory. Geometry optimizatiuons and frequency analysis of various starting structures are performed. The ground state of SinCl and SinCl? (n=1–6) clusters are identified, with nature poplutation, binding energied and electron affinity discussed. The research results indicate that the most stable SinCl and anion isomers keep the same frameworks as the corresponding Sin and Sin+ clusters only with a slight distortion in geometry. The Cl atom is bound to the apex atom in Sin fram, which make the structures more stable. The absorption of an Cl atom onto the Sin cluster leads to a localized charge transfer on Si–Cl bond. The 3p subshell of Cl atom is essentially filled, which indicate the 3p orbital take an active role in the bonding. Furthermore, the Cl atom has sp3 hybrid electron configuration. For the anionic clusters, the most of the extra electron is placed into 3p orbital of Si atom. The binding energy increase dramatically as the size of chlorine doped silicon clusters increase. The binding energy has higher value for SinCl clusters than that of the corresponding anionic clusters, except Si5Cl cluster. It reflects that the stabilities of the neutral SinCl clusters are higher than the corresponding anions.The possible geometries of the SnnCl and SinCl? (n=1–6) clusters are optimized by using ensity functional method. The harmonic vibrational frequencies and total energies are computed. The ground state structures of SnnCl and its anion are obtained. Theoretical results show that the most stable SnnCl and SnnClˉ(n=1–3) have plane structures, while is three-dimensional structures when n=4–6. The Cl atom is bound to one Sn atoms of the Snn cluster and keeps the frame of the corresponding Snn cluster unchanged. Furthermore, Cl–Si bond length in anion is longer than in neutral, due to the additional electron on the antibonding orbital. Natural population and natural electron configurations are discussed. The result indicate charges are transferred mainly from Sn atoms to the Cl atom. The Sn atom directly bound to the Cl atom is positively charged, which indicate that the Sn atom repulse electrons. Fragmentation energies (Fe) of SnnCl and SinCl? (n=1–6) clusters are also computed. the dissociation energies of SinCl (n=1–6) clusters shows odd-even alternation as the clusters size grows, except for Sn3Cl. while the fragmentation energy of SnnCl? (n=1–6) clusters increases as the size of n increases, except for Sn4Cl? cluster. Sn4Cl, Sn6Cl, Sn4Cl? and Sn6Cl? have more stable structures in the two cluster series under investigation, which are similar regularities of the corresponding fragmentation energies of Snn (n=1–6). The electron affinities (EAs) of SnnCl clusters are calculated, good agreement with experimental results available, which prove our theoretical result reliable.
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