闪锌矿结构AlN、AlP、AlAs和AlSb电子结构和光学性质的第一性原理研究

本文采用基于密度泛函理论下的第一性原理平面波赝势从头算量子力学方法,对闪锌矿结构AlN、AlP、AlAs和AlSb的电子结构和光学性质进行了研究.分析比较了这些化合物的能带结构、态密度、介电函数及折射率等性质,总结Al与不同V族元素形成化合物时的性质变化规律.结果表明,四种材料有着相似的能带结构,都是间接带隙宽禁带半导体,但是在导带底AlN的能态结构与其它三种材料明显不同.随着从AlN到AlSb的变化,光学性质曲线向低能端移动(红移趋势).     

Properties of a Si2N molecule under an external electric field

In the present work,we adopt the ccsd/6-31g（d） method to optimize the ground state structure and calculate the vibrational frequency of the Si2N molecule.The calculated frequencies accord satisfactorily with the experimental values,which helps confirm the ground state structure of the molecule.In order to find how the external electric field affects the Si2N molecule,we use the density functional method B3P86/6-31g（d） to optimize the ground state structure and the time-dependent density functional theory TDDFT/6-31g（d） to study the absorption spectra,the excitation energies,the oscillator strengths,and the dipole moments of the Si2N molecule under different external electric fields.It is found that the absorption spectra,the excitation energies,the oscillator strengths,and the dipole moments of the Si2N molecule are affected by the external electric field.One of the valuable results is that the absorption spectra of the yellow and the blue-violet light of the Si2N molecule each have a red shift under the electric field.The luminescence mechanism in the visible light region of the Si2N molecule is also investigated and compared with the experimental data.     

SiN分子外电场情况下的发光特性

为全面分析外电场对分子发光特性的影响, 本文采用密度泛函B3P86方法6-31g(d)基组, 对SiN分子进行了基态结构的优化, 进而使用含时密度泛函方法(time dependent density functional theory, TDDFT), 计算了不同方向及大小的外电场情况下SiN分子的吸收谱、激发能、振子强度、跃迁偶极矩. 通过比较发现外电场对该分子的激发能、吸收谱、跃迁振子强度及跃迁偶极矩影响都比较明显, 说明了电场对SiN分子的激发特性影响比较复杂, 特别是在加场前后分子均有在可见光区波段的吸收谱, 这对研究分子的发光很有意义.同时对该分子所发可见光谱的产生机理进行了分析, 并与已有实验结果进行比较.     

Population coherent control of Rydberg sodium atom in microwave field

The B-spline expansion technique and the time-dependent multilevel approach (TDMA) are used to study the interaction between microwave field and sodium atoms. The Rydberg sodium atom energy levels of p states in zero field are calculated, and the results are in good agreement with the other theoretical ones. The time evolutions during the population transfers of the five states from n=75 to n=79 in different microwave fields are obtained. The results show that the coherent control of the population transfer from the lower states to the higher ones can be accomplished by optimizing the microwave pulse parameters.     

First-Principles Calculations of Elastic and Thermal Properties of Lanthanum Hexaboride

The plane-wave pseudopotentiai method using the generaiized gradient approximation within the framework of density functional theory is applied to anaylse the bulk modulus, thermal expansion coefficient and heat capacity of LaB6. The quasi-harmonic Debye model, using a set of total energy versus volume obtained with the plane-wave pseudopotential method, is applied to the study of the thermal properties and vibrationai effects. We analyse the bulk modulus of LaB6 up to 1500 K. The elastic properties calculations show that our system is mechanically stable. For the heat capacity and the thermal expansion, significant differences in properties are observed above 300K. The calculated zero pressure bulk modulus is in good agreement with the experimental data. Moreover, the Debye temperatures are determined from the non-equilibrium Gibbs functions and compared to available data.     

RbH2PO4不同相的铁电性和光学特性

利用第一性原理系统地研究了RbH2PO4晶格优化结构、总的和分的态密度、电荷密度分布。我们发现氧原子和Rb, H原子的杂化形成了两种离子群,在铁电相离子键和PO4四面体的耦合强度比顺电相更强。结果,通过P-O 和 H-O的距离改变电荷密度的再分布和PO4四面体的顺序旋转导致了铁电性的产生。两种类型粒子群的运动和自动成型畴壁导致了可以观测的焦热电流。     

取代氯苯化合物的电子结构和键离解能的理论研究

利用密度泛函（DFT）三种交换／相关函数（B3LYP,B3PW91,B3P86）结合6—31G^＊＊和 6-311G^＊＊基组,计算了13个取代氯苯化合物的键离解能．结果表明B3PS6／6—311G^＊＊方法是计算取代氯苯化合物键离解能的可信方法,研究发现C—Cl键的键离解能与所使用的基组和计算方法密切相关,取代基对C—Cl键的键离解能的影响不明显．研究了目标化合物的前线轨道能级差,并对取代氯苯化合物的热稳定性做了评估．     

密度泛函方法对SiO分子基态(X 1 Σ+)势能函数的研究

利用密度泛函B3P86方法,分别选用STO-3G,D95**,6-311G,6-311 + + G,6-311 + + G**,cc-PVTZ基组对SiO分子基态(X 1 Σ+)进行结构优化计算.通过比较得出,cc-PVTZ基组为对SiO分子基态(X 1 Σ+)进行结构优化最优基组的结论.使用密度泛函B3P86方法,选用cc-PVTZ基组进行单点能扫描,用正规方程组拟合SiO分子基态(X 1 Σ+)的Murrell-Sorbie函数,得到解析势能曲线.最后,由得到的解析势能函数计算了相对应的光谱常数(Be,αe,ωe和ωeχe),并与实验值进行了比较.     

O2的外电场效应研究

本文首先采用多种方法,分别在不同的基组水平下,对O2的几何构型进行了优化,然后用密度泛函(DFT)(b3p86)方法在6-31G(d)基组水平上,在不同的外电场作用下,对O2的平衡结构进行了优化计算.在得到稳定几何构型的基础上,计算和讨论了偶极外电场对O2基态的几何构型、电偶极矩、原子电荷数的分布、振动频率、轨道能级分布等性质的影响.     

外电场作用下SiO电子结构特性研究

在得到SiO分子基态稳定构型的基础上，选用B3P86/6-311++g(d，p)方法优化得到了不同外电场(-0.03—0.03a.u.)下SiO分子基态的稳定电子结构，研究了外电场对SiO分子基态键长、能量、电荷分布、能级分布，能隙及红外光谱的影响规律.结果表明，分子结构与电场呈现强烈的依赖关系，且对电场的方向依赖呈现出不对称性.同时在正向外电场逐渐增大的过程中，SiO分子能隙始终处于减小趋势，占据轨道的电子易于激发至空轨道，因而为研究材料的电致发光机理奠定了一定的理论基础.