兰州大学机构库 >物理科学与技术学院
金及其合金团簇的结构和非线性光学性质
Alternative TitleStructural and Nonlinear Optical Properties of Aun-mXm (X = Ag, Cu) Clusters
许莹
Thesis Advisor徐灿
2009-05-29
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword金的合金团簇 非线性光学性质 密度泛函理论 密度泛函理论
Abstract金团簇在电子设备、功能纳米材料、光学材料、催化剂等方面有广阔的应用前景,人们从实验和理论上对金团簇进行了大量的研究,主要包括基态结构、电子结构、催化、吸附和非线性光学效应等方面。 金团簇有可观的非线性光学特性,可以作为一些光学器件的基本材料。本文使用第一性原理计算并讨论金团簇非线性光学性质,并且讨论在金团簇中掺杂银或铜原子对其结构、电子性质以及一阶超极化率的影响。文章从掺杂位置、杂质浓度、团簇尺寸和杂质原子种类等方面全面讨论了掺杂银或铜原子对金团簇非线性光学性质的影响。全文主要分为两个部分: 1. 平面金及其合金团簇的构型和非线性光学性质 用密度泛函理论中B3LYP方法在LanL2DZ基组水平上对Aun (n = 10, 16)团簇及其合金团簇Aun-mXm (X = Ag, Cu; m = 1, 2)的几何结构、电子性质以及非线性光学性质进行了理论研究。结果表明掺杂对团簇的几何结构以及能隙值影响较小,但是可以显著增大团簇的非线性光学参数。掺杂使团簇的一阶超极化率增大,原因之一是杂质原子破坏了团簇原有的对称中心。在同一基组水平上利用含时密度泛函理论分析合金团簇的非线性光学性质,结果显示掺杂增大了团簇基态到激发态跃迁的电子偶极矩变化,并且增大了跃迁矩,这两个因素共同作用使结构的二阶非线性光学系数增大。增加杂质原子的数目也可以使团簇的非线性光学系数增大,因为杂质原子在团簇中起到电子给体的作用。增大团簇尺寸同样能使一阶超极化率增大。 上述效应能够用来为非线性光学应用设计高效的金团簇材料。 2. 四面体Au20团簇及其合金团簇的构型和非线性光学性质 用PBE方法在LanL2ZD基组水平优化得到四面体Au20基态几何结构,并计算出该结构的能隙、平均结合能。用银或铜元素分别取代四面体Au20团簇中不同位置的金原子,进行几何优化计算,得到六种四面体Au20的掺杂团簇:Agvertex, Agedged, Agcenter, Cuvertex, Cuedged, Cucenter。计算四面体Au20团簇以及六种掺杂团簇的一阶超极化率,并加以分析。 掺杂对能隙和平均结合能等性质影响很小,但可以较大程度改变团簇的一阶超极化率。顶点掺杂的团簇一阶超极化率值大于四面体Au20团簇,棱边掺杂以及面心掺杂的团簇,其值均小于四面体Au20团簇。原因是四面体Au20棱边原子到顶点原子的正电荷转移使其具有强一阶非线性光学特性,顶点掺杂银原子可以加剧这种电荷转移,因为银原子比金原子更易失去电子,棱边原子的正电荷向顶点的银原子转移程度较强,使Agvertex团簇一阶超极化率值高于Au20团簇。在非顶点位置掺杂银原子都会使电荷转移过程受阻,因此棱边掺杂和面心掺杂团簇的一阶超极化率小于四面体Au20团簇。掺杂铜原子的团簇与掺杂银原子的团簇相似,但由于铜原子的失电子能力弱于银原子,其一阶超极化率的变化程度小于掺杂银的团簇。
Other AbstractBecause of their physical and chemical behavior, gold clusters have been widely applied in electronic equipment, functional nano material, optical material and catalyst fields. Large numbers of experimental and theoretical investigations have been processed, including structural characteristics, electronic properties, catalytic properties, adsorption effects and nonlinear optical properties researches. Gold clusters can be served as material of optical devices for their great nonlinear optical properties. In this thesis, first-principle calculations are used to obtain the nonlinear optical parameters of gold-based clusters. The effect on structural characteristics, electronic properties and nonlinear optical properties of doping Ag or Cu atoms into pure gold clusters are discussed. The influence of doping position, impurity consistence, size effect and dissimilarity of doping Ag or Cu atoms are discussed. This thesis is arranged as following two parts: 1. Structural characteristics and nonlinear optical properties of planar gold-based clusters Pure Aun (n = 10, 16) and their alloyed clusters Aun-mXm (X = Ag, Cu; m = 1, 2) are theoretically investigated for the structural characteristics, electronic properties, and nonlinear optical properties using density-functional theory (DFT) at B3LYP/LanL2DZ level. Doping exhibits little effect on geometric structural characteristics and energy gaps but enormous augmenting of the second-order nonlinear optical (NLO) coefficients. The primary causation of the enhancement of β is the lack of centro-symmetry feature in these alloyed clusters. Time-dependent density-functional theory (TD-DFT) analysis at the same basis set show doping increases the ground to excited state transition electric dipole moments and transition dipoles, which make important roles in enhancing the second-order NLO coefficients. Increasing number of X atoms increases the NLO coefficients of clusters because the X atoms act as electron donors in alloyed clusters. Increasing the length of clusters can also augment the β values in our investigation. The reported effect can be utilized to design effective gold-based alloyed clusters for NLO applications. 2. Structural characteristics and nonlinear optical properties of tetrahedral Au20 cluster and its alloyed clusters The PBE method is used to calculate the ground structures, energy gaps and binding energies of tetrahedral Au20 cluster and its alloyed clusters at LanL2DZ level. Three different A...
URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/229712
Collection物理科学与技术学院
Recommended Citation
GB/T 7714
许莹. 金及其合金团簇的结构和非线性光学性质[D]. 兰州. 兰州大学,2009.
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