CdTe和HgTe电子结构的紧束缚模型计算

基于局域密度近似(LDA或GGA)的密度泛函理论计算往往低估体系的禁带宽度,而这一低估对窄带隙半导体尤为严重.尽管基于混合泛函的密度泛函理论能有效地修正这一误差,但是由于计算量较大仍无法用于计算较大体系.本文发展了一组能够比较准确描述CdTe和HgTe晶体电子结构的紧束缚参数.将基于混合泛函的密度泛函计算结果作为输入,我们构建了正交的sp~3s~*基组下的紧束缚模型.此模型能够比较准确地描述能带结构在费米面附近4 eV范围内的色散关系.利用当前模型计算了CdTe和HgTe非晶的电子态密度,计算结果与他人的理论计算和实验值符合较好.     

含时密度泛函理论及应用的最新发展

密度泛函理论在材料计算研究领域得到了广泛的应用,然而它无法处理含时问题和材料的激发态性质。Runge-Gross定理奠定了含时密度泛函理论的基础,为研究这两类问题提供了有效的手段。经过三十多年的发展,含时密度泛函已被应用到量子化学、材料计算等多个领域,人们也更加了解其优势和不足。目前,含时密度泛函理论和方法仍在迅速发展。本文简要回顾含时密度泛函方法的发展历史,介绍近年来含时密度泛函在理论和应用方面的一些重要进展,总结当前在含时密度泛函领域存在的重要难题以及面临的挑战,展望其发展方向和趋势。     

铝原子团簇Al5、Al5-和Al5+稳定结构的密度泛函理论研究

采用密度泛函理论的四种方法 :杂化密度泛函B3LYP与B3PW 91、Perdew Wang91交换与相关泛函WP91PW91、局域自旋密度近似SVWN ,研究了Al5、Al5-和Al5+ 团簇的多种可能结构 ,找到了它们稳定的结构与自旋态 ,与已有的理论结果作了比较 ,并计算了Al5-的绝热与垂直电子离解能、Al5的绝热与垂直电离势 ,同有关的实验数据比较 ,符合较好 .同时对四种密度泛函方法的计算结果作了一些比较与讨论     

Density Functional Study on Relative Energies, Structures, and Bonding of Low-lying Electronic States of Lutetium Dimer

用密度泛函理论方法研究了镥二聚体(Lu₂)低能量电子态的性质,计算了电子态相对能量、平衡键长、振动频率以及基态解离能,考察了密度泛函性质、相对论有效势种类以及Hartree-Fock交换作用大小对计算结果的影响．结果表明,无论采用何种密度泛函和相对论有效势,体系的基态都为三重态,与其他一些基于分子轨道理论的从头计算方法得到的结论是一致的．另外,与分子轨道从头计算结果以及实验结果比较发现,采用杂化密度泛函理论和Stuttgart小核有效势计算得到的结果总体吻合最好．最后,特别分析研究了B3LYP计算中Hartree-Fock交换作用大小对基态键长和基态解离能的影响,发现随着交换作用的增大,键长增长,解离能减小,这是由于5d轨道杂化导致的共价成键作用减弱造成的．     

基于第一性原理研究单壁碳纳米管的力学性质

用基于第一性原理的Crysta103软件中的Hartree-Fock近似和密度泛函与Hartree-Fock混合近似两种方法计算一系列碳纳米管的杨氏模量,对两种近似方法的计算结果进行比较.Hatree-Fock近似计算的杨氏模量与实验和其它理论结果符合较好;密度泛函和Hartree-Fock混合近似计算的杨氏模量偏小,...     

约束条件下的硬球流体

利用密度泛函理论和分子动力学方法 ,对处于两平行硬墙之间的硬球流体的密度分布进行了计算 .通过比较两种方法的结果 ,发现在墙之间距离较大时 ,Rosenfeld密度泛函理论的结果与分子动力学模拟的结果符合很好 ;当两堵墙间的距离很小时 ,这两个结果之间存在明显的不一致 .另外 ,还研究了约束条件下密度分布的结构     

高压下钒的结构相变及熔化温度的第一性原理计算

本文基于第一性原理的密度泛函理论（DFT）和密度泛函微扰理论（DFPT）,优化计算出金属钒在不同压强下的晶体结构,以此来说明其发生的结构相变。最后利用晶体结构和能量的关系,直接导出钒在不同压强下的熔化温度。计算结果都与已有的结果进行了比较。     

高压下钒的结构相变及熔化温度的第一性原理计算

本文基于第一性原理的密度泛函理论(DFT)和密度泛函微扰理论(DFPT),优化计算出金属钒在不同压强下的晶体结构,以此来说明其发生的结构相变.最后利用晶体结构和能量的关系,直接导出钒在不同压强下的熔化温度.计算结果都与已有的结果进行了比较.     

用含时密度泛函理论计算钠原子跃迁光谱

运用含时密度泛函理论和局域密度近似方法，计算出了Na原子的多个激发态能级和各能级电子波函数的实空间分布，并从中分析出其跃迁光谱Rydberg序列的主要特征谱线. 计算结果与实验数据符合得较好，充分验证了密度泛函激发态理论的有效性. 关键词： TDDFT 激发态 跃迁光谱 Na原子     

Density Functional Theory Study of Infrared and Ultraviolet Spectra of Urea L-Malic Acid

用密度泛函理论研究了新型二阶非线性光学晶体-L苹果酸脲.采用一些密度泛函理论方法计算了分子结构,比较得出PBEPBE/6-31+G(d,p)是计算分子结构的一种最佳的方法,然后给出了其红外和紫外可见光谱,并与实验结果作了比较,还结合分子轨道布局分析了紫外可见光谱. 同时结合极化连续模型利用密度泛函理论方法研究了L苹果酸脲在水中的几何结构及红外和紫外可见光谱,并指出了溶剂化效应对其性质的影响.     

Towards a description of the Kondo effect using time-dependent density-functional theory

We demonstrate that the zero-temperature conductance of the Anderson model can be calculated within the Landauer formalism combined with static density-functional theory. The proposed approximate functional is based on finite-temperature density-functional theory and yields the exact Kohn-Sham potential at the particle-hole symmetric point. Furthermore, in the limit of zero temperature it correctly exhibits a derivative discontinuity which is shown to be essential to reproduce the conductance plateau. On the other hand, at the Kondo temperature the exact Kohn-Sham conductance overestimates the real one by an order of magnitude. To understand the failure of density-functional theory, we resort to its time-dependent version and conclude that the suppression of the Kondo resonance must be attributed to dynamical exchange-correlation corrections.     

A comparison of density-functional-theory and coupled-cluster frequency-dependent polarizabilities and hyperpolarizabilities

The frequency-dependent polarizabilities and hyperpolarizabilities of HF, CO, H₂O and para-nitroaniline calculated by density-functional theory are compared with accurate coupled-cluster results. Whereas the local-density approximation and the generalized gradient approximation (BLYP) perform very similarly and overestimate polarizabilities and, in particular, the hyperpolarizabilities, hybrid density-functional theory (B3LYP) performs better and produces results similar to those obtained by coupled-cluster singles-and-doubles theory. Comparisons are also made for singlet excitation energies, calculated using linear response theory.     

Application of Lanczos-based time-dependent density-functional theory approach to semiconductor nanoparticle quantum dots

We present a density-functional theory study of Si nanoparticle quantum dots, focusing on determination of their optical properties. To calculate the absorption spectra of our quantum dot models we use a recently-developed method based on the application of Lanczos algorithms to linear-response time-dependent density-functional theory (LR-TDDFT). Quantum dot models are obtained by cutting Si atoms from the bulk crystal lattice and adding appropriate H terminating atoms to the surface; these structures are relaxed using density-functional theory in the plane-wave pseudopotential supercell approach, and then absorption spectra are calculated. We verify that with increasing size of the nanoparticle, the optical gap/onset of absorption steadily moves to lower energies. The paper represents an important demonstration of this new methodology on a class of systems that are the focus of significant current research in nanoscience.     

Classical multicomponent fluid structure near solid substrates: Born-Green-Yvon equation versus density-functional theory

We report a study of adsorption of binary mixtures of hard spheres of different sizes on a hard wall by using a version of density-functional theory, the Born-Green-Yvon (BGY) equation and Monte Carlo simulations. Following the BGY approach introduced by Fischer and Methfessel for single-component fluids, the proposed extension uses coarse-grained densities to approximate the contact values of pair distribution function of hard spheres. A procedure for evaluation of the coarse-grained densities, leading to an exact theory in one dimension, is proposed. The density-functional theory employed here, however, uses the Meister-Kroll and Groot approach. Comparisons of theoretical calculations with Monte Carlo simulations, as well as with previous theoretical predictions, have shown that density-functional theory reproduces the pseudo-experimental data accurately, even for extremely large size ratios of molecules of both species. The accuracy of the predictions of the BGY approach is less satisfactory, and for higher bulk fluid densities discrepancies with numerical simulations have been found.     

Structures,stabilities, and electronic properties of F-doped Sin （n=1～12） clusters：Density functional theory investigation

The geometries, stabilities, and electronic properties of FSin （n=1～12） clusters are systematically investigated by using first-principles calculations based on the hybrid density-functional theory at the B3LYP/6-311G level. The geometries are found to undergo a structural change from two-dimensional to three-dimensional structure when the cluster size n equals 3. On the basis of the obtained lowest-energy geometries, the size dependencies of cluster properties, such as averaged binding energy, fragmentation energy, second-order energy difference, HOMO–LUMO （highest occupied molecular orbital–lowest unoccupied molecular orbital） gap and chemical hardness, are discussed. In addition, natural population analysis indicates that the F atom in the most stable FSin cluster is recorded as being negative and the charges always transfer from Si atoms to the F atom in the FSin clusters.     

Time-dependent density-functional theory beyond the local-density approximation

Approximations for the ground-state exchange-correlation potential of density-functional theory have reached a high level of sophistication. By contrast, time- or frequency-dependent exchange-correlation potentials are still being treated in a local approximation. Here we propose a novel approximation scheme, which effectively brings the power of the generalized gradient approximation (GGA) and meta-GGA to time-dependent density-functional theory. The theory should allow a more accurate treatment of strongly inhomogeneous electronic systems (e.g. molecular junctions) while remaining essentially exact for slowly varying densities and slowly varying external potentials.     

Efficient approach to time-dependent density-functional perturbation theory for optical spectroscopy

Using a superoperator formulation of linearized time-dependent density-functional theory, the dynamical polarizability of a system of interacting electrons is represented by a matrix continued fraction whose coefficients can be obtained from the nonsymmetric block-Lanczos method. The resulting algorithm, which is particularly convenient when large basis sets are used, allows for the calculation of the full spectrum of a system with a computational workload only a few times larger than needed for static polarizabilities within time-independent density-functional perturbation theory. The method is demonstrated with calculation of the spectrum of benzene, and prospects for its application to the large-scale calculation of optical spectra are discussed.