| Summary: | 碩士 === 淡江大學 === 化學學系碩士班 === 94 === The optimized geometries and the electronic structures of hydrogenated silicon clusters which include the Td and Ih symmetries, were generated by using the semi-empirical AM1, and PM3 methods, the density functional theory (DFT) B3LYP method with the 6-31G* and the LANL2DZ basis sets as well as the local density functional approximation (LDA) implemented in SIESTA package. The Td symmetry hydrogenated silicon clusters with Si5H12 up to Si281H172 were used in this study. For the Ih symmetry, we calculated Si20H20, Si100H60 and Si280H120 clusters only. Theoretically, the energy gap between HOMO and LUMO is size dependent. The calculated energy gap is decreased while the diameter of silicon cluster is increased. Compared different calculated results, we conclude that the calculated energy gap by DFT B3LYP//SIESTA is closed to that of experimental data. LDA/SIESTA result is underestimate to the experiments. Contrarily, the AM1//SIESTA and PM3//SIESTA results are overestimate to the experiments. For the investigation of substituent effect, the calculated energy gap of Si35H36 is closed to that of Si35(CH3)36 and is higher than that of Si35(OH)36. Concludly, the electron-withdrawing group may increase the energy gap of silicon cluster.
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