Cluster growing process and a sequence of magic numbers

We present a new theoretical framework for modeling the cluster growing process. Starting from the initial tetrahedral cluster configuration, adding new atoms to the system, and absorbing its energy at each step, we find cluster growing paths up to the cluster sizes of more than 100 atoms. We demonstrate that in this way all known global minimum structures of the Lennard-Jones (LJ) clusters can be found. Our method provides an efficient tool for the calculation and analysis of atomic cluster structure. With its use we justify the magic number sequence for the clusters of noble gas atoms and compare it with experimental observations.     

基于克隆选择的混合遗传算法在碳纳米管结构优化中的研究

针对分子动力学模拟中碳纳米管的结构优化问题，提出了一种新的优化算法.新的优化算法在遗传算法的基础上，引入了克隆选择机理和模拟退火技术.对五个典型函数的优化测试结果表明，该算法搜索过程稳定性好，可较好地实现全局最优.将其应用于碳纳米管原子结构优化，加快了能量优化速度，提高了优化质量.模拟结果说明，混合遗传算法的优化时间随原子数增加而呈线性增长.在碳纳米管原子数较多时，结构优化时间比共轭梯度法降低一个数量级左右，大大降低了系统的模拟时间. 关键词： 分子动力学 碳纳米管 能量优化 遗传算法 克隆选择算法     

AlnMgm (n+m=6,7;m=1,2)团簇的稳定性与电子结构

用遗传算法结合经验势对AlnMgm(n+m=6,7; m=1,2)的低能结构进行全局搜索,用从头计算方法研究了其稳定性和电子结构。计算表明AlnMgm存在多个能量相近的异构体,在AlMg团簇中Mg-Mg相互作用远弱于Al-Al作用,稳定结构中Mg原子倾向于形成更多的Mg-Al键。NBO电荷分析表明Mg向Al转移电子,Al原子上的电荷大小强烈依赖于相连的Mg原子个数。电子结构分析表明随着原子数目的增大,占据轨道能级略有降低,同尺寸下掺杂一个Mg时能级更低;AlMg团簇的能隙约为5.30 eV。     

Al_nMg_m(n+m=6,7;m=1,2)团簇的稳定性与电子结构

用遗传算法结合经验势对AlnMgm(n+m=6,7;m=1,2)的低能结构进行全局搜索,用从头计算方法研究了其稳定性和电子结构.计算表明AlnMgm存在多个能量相近的异构体,在Al Mg团簇中Mg-Mg相互作用远弱于Al-Al作用,稳定结构中Mg原子倾向于形成更多的Mg-Al键.自然键轨道(NBO)电荷分析表明Mg向Al转移电子,Al原子上的电荷大小强烈依赖于相连的Mg原子个数.电子结构分析表明随着原子数目的增大,占据轨道能级略有降低,同尺寸下掺杂一个Mg时能级更低;Al Mg团簇的能隙约为5.30 e V.     

Calorimetry at surfaces using high-resolution core-level photoemission

We have developed a method to measure simultaneously the internal energy of bulk and the first layer atoms of a crystal. The internal energy of bulk and the surface atoms of lithium (110) have been evaluated from 22 K up to above the melting transition, applying the Debye model to the thermal broadening of the respective 1s photoemission lines. Our measurements clearly reveal two phase changes: the known liquid to solid transition and the surface melting, occurring 50 K below the bulk melting point.     

Structural and energetic properties of sodium clusters

In this work we present results from a theoretical study on the properties of sodium clusters. The structures of the global total-energy minima have been determined using two different methods. With the parameterized density-functional tight-binding method (DFTB) combined with a genetic-algorithm we investigated the properties of Na_N clusters with cluster size up to 20 atoms, and with our own Aufbau/Abbau algorithm together with the embedded-atom method (EAM) up to 60 atoms. The two sets of results from the independent calculations are compared and a stability function is studied as function of the cluster size. Due to the electronic effects included in the DFTB method and the packing effects included in the EAM we have obtained different global-minima structures and different stability functions.     

改进的Numerov格式用于Rydberg原子结构的计算

为解决原子Rydberg态的数值计算问题,提出一种改进的Numerov算法.利用此算法计算了H原子n=10,20,……90,100各Rydberg态的能级值和平均半径,并与严格理论值进行了比较.研究结果表明,通过选择适当的Numerov格式,可得到所要求精度的能级和波函数.这为Rydberg原子的进一步研究提供了有效的计算方法.     

The structure and energetics of carbon-nitrogen clusters

The structures and energies of clusters of carbon and nitrogen with up to 12 atoms have been investigated by density functional theory using the hybrid B3LYP functional and the cc-pVTZ basis set. This is the first systematic study of these clusters. Geometries are reported for the lowest energy states at this level of theory. Linear structures tend to be the global minima for clusters containing one or two nitrogen atoms, and patterns in the electronic structure of these clusters are reported. More complex branched structures lie close in energy to the linear conformations and, for clusters greater than six atoms and containing three or more nitrogen atoms, these branched structures are the minimum energy conformers. Comparisons are made with pure carbon and silicon-carbon clusters.     

蛋白质折叠的非格子模型

用粒子群算法对蛋白质的简化模型进行研究,体系中各原子间的相互作用由一物理势表示.通过全局优化体系的势函数得到蛋白质的结构数据,与实验测得的结构数据之间的均方根偏差RMSD为6.12(A).记录了能量最小值及回转半径随程序运行步骤的变化以及RMSD值与最低能量值的分布关系,这些结果反映了蛋白质折叠的一些基本特征.     

Parameter estimation for hysteretic systems

The differential system characterization of hysteretic system is well known. The problem of estimating the parameters of this system on the basis of input-output data, possibly noise corrupted, is considered. It turns out that the estimation problem is a non-linear optimization problem. The Gauss Newton method is used in setting up a two-stage iterative least squares algorithm. The usefulness of the algorithm is validated through its application to various simulated time histories from the hysteretic model.     

First principle study of free and surface terminated CdTe nanoparticles

Density functional calculations of structural and electronic properties of stoichiometric and nonstoichiometric CdTe clusters, containing up to few tens of atoms, are carried out using projector augmented wave method. Molecular dynamics has been performed for Cd₁₂Te₁₂ and Cd₁₅Te₁₅ to predict the structure corresponding to global energy minimum. Cage type structures and bulk fragments, both in zinc blende and wurtzite structures, are used as starting geometries and conjugate gradient method is used to locate the local energy minima for other clusters. The aim of these calculations is to get the energetically favorable probable structures, to be compared with the experimentally known structures. Clusters are relaxed both in vacuum and in the presence of surface passivating ligands and the resulting structural rearrangement is analyzed. As expected, passivation increases the stability of an individual cluster, as indicated by specific properties like binding energy, vertical detachment energy, electron affinity etc. Passivation also locks the symmetry for three-dimensional structures but the small Cd_nTe_n (1 ≤ n ≤ 6) clusters, which are planar, attain higher symmetry structures on passivation. We observe `self-healing' mechanism viz., opening of optical gap on relaxation without the aid of passivating ligand, in CdTe clusters as observed in CdSe clusters [A. Puzder et al., Phys. Rev. Lett. 92, 217401 (2004)]. However, we note that 'self-healing' is a stoichiometry dependent phenomenon. Te atoms are found to achieve a total coordination of 4 on passivation, a fact useful in chemical synthesis of nanoclusters.     

Quasi-physical Algorithm for Protein Folding in an Off-Lattice Model

We study a three-dimensional off-lattice protein folding model, which involves two species of residues interacting through Lennard-Jones potentials. By incorporating an extra energy contribution into the original potential function, we replace the original constrained problem with an unconstrained minimization of a mixed potential function. As such an efficient quasi-physical algorithm for solving the protein folding problem is presented. We apply the proposed algorithm to sequences with up to 55 residues and compare the computational results with the putative lowest energy found by several of the most famous algorithms, showing the advantages of our method. The dynamic behavior of the quasi-physlcal algorithm is also discussed.     

基于混合交叉进化算法的混沌系统参数估计

提出一种混合交叉进化算法 来估计混沌系统的未知参数. 首先通过构造一个适当的适应度函数, 将混沌系统的参数估计问题转化为一个多维的优化问题. 在混合交叉进化算法中, 利用佳点集方法初始化种群, 增加了算法的稳定性和全局搜索能力. 在进化过程中, 混合交叉操作既能指导种群个体向最优解子空间靠近, 又能提高算法跳出局部最优的能力, 从而协调了算法的勘探和开采能力. 以几个标准测试函数和典型的Lorenz混沌系统为例进行仿真实验, 结果表明了该方法的有效性.     

类锂离子里德堡态中的自旋-其它轨道相互作用

以多电子原子精细结构哈密顿的球张量形式和三价原子的非相对论性能级结构理论为基础,借助不可约张量理论,建立了计算类锂离子里德堡态中的自旋-其它轨道相互作用能的一种解析理论形式.完成了所有的角向积分和自旋求和计算,自旋-其它轨道相互作用能最终用径向积分来表示.应用所建立的理论对类锂离子(1s2np)2Pj态的自旋-其它轨道相互作用能进行了具体分析.     

无线携能通信系统中基于能量获取比例公平的波束成形设计

针对无线携能通信系统中存在能量获取不均衡的问题, 提出了一种基于能量获取比例公平的波束成形设计方案. 该方案在满足信息接收者的信干噪比以及发送端的最大发送功率等约束条件的基础上, 通过优化波束矢量实现能量获取的比例公平. 此设计在数学上是一个很难直接求解的非凸优化问题.为此, 本文首先利用半定松弛技术将其转换为半定规划问题, 然后结合二分法提出了可以获得最优波束矢量的迭代算法.此外, 在发送端仅知道部分信道状态信息且知道信道误差范围的情况下, 采用最差性能最优的方法对原优化问题进行了鲁棒波束成形设计, 并提出了相应的迭代算法. 仿真结果表明所提算法均可实现能量获取的比例公平且性能达到全局最优.     

Predominant environmental noise classification over sound mixing based on source-specific dictionary

This paper presents a methodology to classify predominant urban acoustic sources in real mixed signals. This is based on a source-specific dictionary with atoms in the time–frequency domain using the Orthogonal Matching Pursuit (OMP) algorithm and identifying the class through a proposed selection criterion with a dynamic number of iterations involving a lower algorithm complexity. Several time–frequency atoms were evaluated considering retained energy and relative error to build a source-specific dictionary in the relevant classes. The source-specific dictionary has better results up to 7% in retained energy than to use an individual dictionary such as based on wavelet or Gabor functions, improving classification of predominant sources over sound mixing up to 9% compared to using standard dictionaries. Experimental results on classification are applied to mixture inter-class signals of two or more sources recorded by a real permanent monitoring system in an urban soundscape. The classification performance has successfully achieved identifying a predominant source in real inter-class mixtures of urban soundscapes.     

探地雷达反问题的小波-同伦混合反演算法

构造一种求解探地雷达反问题的小波-同伦混合反演算法.利用小波将反问题分解到不同尺度上,在最大尺度上采用同伦反演方法,求得次级尺度的初始近似解,在其余尺度上进行多次迭代修正,以获得全局最小点.算法结合小波反演和同伦反演的优点,数值结果表明其具有较强的全局搜索能力.     

类硼离子基态的精细结构(英文)

以多电子精细结构哈密顿的球张量形式为基础,借助不可约张量理论,建立了类硼离子基态精细结构能量的解析表达式.完成了所有角向积分和自旋求和计算,使精细结构能量表示为若干个径向积分之和.在此基础上计算了类硼体系(Z=5~8)基态精细结构能量,计算结果与实验数据符合得较好.     

基于改进型模拟退火模型的X荧光光谱寻峰方法的研究

在能量色散X荧光分析技术分析中,对谱信息的处理一直是研究的重点,谱光滑、寻峰、峰面积处理都是重中之重,本工作基于模拟退火算法原理,建立一种新的寻峰模型算法,该算法利用模拟退火寻找全局最优点的收敛特性,以Metropolis准则作为峰谷判断的基础,引入新的判定标准和峰谷数组,同时从谱道址两端同时收敛,以收敛到同一最优解为终止条件。同时,利用该算法与简单比较法、三阶导数法进行对比实验,结果证明该算法在X荧光光谱寻峰中有较强能力,在实际生产中具有一定价值。