【作者】 楚合营；

【导师】 李蕴才；

【作者基本信息】 河南大学 ， 凝聚态物理， 2007， 硕士

【摘要】 本论文在第一章介绍了计算材料科学中几种主要的计算方法;在第二章介绍了Dmol³和CASTEP模拟软件所基于的理论基础;在第三章简要介绍了基于密度泛函理论的模拟软件包Dmol³中的一些参数,并对利用Dmol³研究的CdnSn（n≤9）团簇的最低能量结构和电子性质进行了理论分析;在第四章介绍了利用基于第一性原理的超软赝势软件包CASTEP模拟的S掺杂纤锌矿ZnO所形成的纤锌矿ZnO_1-xS_x化合物的带隙随S掺杂量的增加先减小后增加的原因。我们在广义梯度近似和全电子非限制自旋的基础上对硫化镉团簇进行结构优化和电子性质模拟,计算结果表明CdnSn（n≤9）团簇的最低能量结构:当n=2,3时为二维环状结构;当n=4-9时为三维笼状结构。更有意思的是这些三维笼状结构可以看成是由Cd₂S₂和Cd₃S₃团簇的最低能量结构组合而成。Cd_nS_n（n≤9）团簇的总能量二阶有限差分和能隙都显示,团簇的幻数为3和6。当n=9时,最低能量结构下的硫化镉团簇的大小为0.72 nm。这和试验上制备的硫化镉量子点的大小具有一定的可比性。研究硫化镉团簇可以为我们理解硫化镉量子点的微观生长机理以及发光特性等提供理论依据。在使用CASTEP模拟软件包研究本征纤锌矿ZnO、ZnS以及S掺杂ZnO所形成的纤锌矿ZnO_1-xS_x化合物的电子性质时,我们的计算结果显示纤锌矿ZnO_1-xS_x化合物的晶格常数随S的掺杂量的增加呈线性增加关系;S 3p态电子决定价带顶的位置,且基本上不因S含量的改变而发生位移; Zn 4s态电子决定导带底的位置,并随S掺入量的增加先向低能端移动而后向高能端移动。我们认为由于S^2-阴离子半径大于O^2-阴离子半径,随着S^2-取代纤锌矿ZnO中的O^2-的不断增加造成ZnO_1-xS_x化合物的晶体畸变先增加而后减少是造成ZnO_1-xS_x化合物带隙先减小而后增加的根本原因。更多还原

【Abstract】 In this dissertation, Computational Materials Science has been introduced in the firt chapter; in the second chapter, Density Functional Theory is introduced, which is the groundwork of Dmol³ and CASTEP packages; the lowest-energy structures and partial electronic properties of CdnSn （n≤9） clusters have been studied by Dmol³ package in the third chapter ; in the end chapter, the electronic structures of wurtzite ZnO, ZnS and S doped ZnO have been investigated by using first-principles ultrasoft pseudopotential modeling package—CASTEP.The lowest-energy structures and electronic properties of CdnSn （n≤9） clusters have been studied by using the generalized gradient approximation and all electron spin-unrestricted methods. Two dimensional ringlike structures have been found to be the lowest-energy configurations in the case of the smaller calculated clusters at n=2 and 3, and three dimensional spheroid configurations for the larger ones at n=4-9. It is especially interesting that the three dimensional structures may be imagined as being built from the Cd₂S₂ and Cd₃S₃ rings. Calculations show that the magic numbers of CdnSn （n≤9） clusters are n=3 and 6. The size of the lowest energy structure of Cd₉S₉ is about 0.72 nm.The electronic structures of wurtzite ZnO, ZnS and S doped ZnO have been investigated by CASTEP package. The calculation results indicate:the crystal constants increase with the quantity of S doping wurtzite ZnO; the top position of the valence band is determined by the S 3p electron state and it does not shift with the thickness of S-doping; the bottom position of the conduction band is determined by the Zn 4s electron state and it can shift to a lower energy position at first and then shift to a higher energy position with increasing S concentrations, the band gap of ZnO_1-xS_x is least when x is equal to 0.5. It is essential reason that the aberration of the crystal structure change with the thickness of S doping wurtzite ZnO.更多还原