Ge(SiO2)n团簇结构和电子性质的密度泛函理论研究

采用密度泛函理论中的广义梯度近似(GGA)对Ge(SiO2)n (n = 1—7)团簇的几何构型进行优化,并对能量、频率和电子性质进行了计算。 结果表明,Ge(SiO2)n的最低能量结构是在(SiO2)n端位O原子以及近邻端位O原子的Si原子上吸附一个Ge原子优化得到;随着锗原子数的增加,增加的锗原子易与原来的锗原子形成锗团簇。掺杂锗原子后团簇的能隙比(SiO2)n团簇的能隙小,当多个Ge原子掺杂到(SiO2)3团簇时,其能隙随着Ge原子个数的增加出现了振荡,Gem(SiO2)3的能隙从可见光区到近红外光区变化。二阶能量差分、分裂能表明Ge(SiO2)2和Ge(SiO2)5团簇是稳定的。     

Ge( SiO2)n团簇结构和电子性质的密度泛函理论研究

采用密度泛函理论中的广义梯度近似(GGA)对Ge(SiO2)n(n=1～7)团簇的几何构型进行优化,并对能量、频率和电子性质进行了计算.结果表明,Ge(SiO2)n的最低能量结构是在(SiO2)n端位O原子以及近邻端位O原子的Si原子上吸附一个Ge原子优化得到;随着锗原子数的增加,增加的锗原子易与原来的锗原子形成锗团簇.掺杂锗原子后团簇的能隙比(SiO2)n团簇的能隙小,当多个Ge原子掺杂到(SiO2)3团簇时,其能隙随着Ge原子个数的增加出现了振荡,Gem(SiO2)3的能隙从可见光区到近红外光区变化.二阶能量差分、分裂能表明Ge(SiO2)2和Ge(SiO2)5团簇是稳定的.     

微锗掺杂直拉单晶硅中的锗-空位复合体

利用第一性原理研究了微锗掺杂直拉单晶硅中的锗和微缺陷的相互作用, 其中微缺陷用一个空位、两个空位和三个空位模拟. CASTEP计算了锗与一个空位、两个空位和三个空位相互作用的情况, 通过分析三种情况下锗与空位(或空位组中心)的间距及空位面积(或体积)的大小, 分别给出了三种情况下最稳定的锗-空位复合体结构模型. 计算表明在微锗掺杂硅单晶中由于锗的引入, 空位容易团聚在锗原子附近, 形成锗-空位复合体.     

二甲基亚锗基锗烯与乙醛生成螺锗杂环化合物反应机理的密度泛函理论研究

用B3LYP/6-31G*方法研究了单重态二甲基亚锗基锗烯(Me₂Ge=Ge:)与乙醛环加成反应的反应机理,根据该反应的势能面可以预言,该反应有一条主反应通道. 该反应所呈现的反应规律为：两反应物通过[2+2]环加成反应首先生成了一锗杂四元环锗烯,由于该锗杂四元环锗烯中Ge:原子的4p空轨道与乙醛的?轨道形成了π→p授受键,从而使锗杂四元环锗烯进一步与乙醛结合生成了一中间体. 由于该中间体中的Ge:原子在过渡态之后发生了sp³杂化,从而使该中间体经过渡态异构化为了一螺锗杂环化合物. 该研究结果从理论上揭示了单重态二甲基亚锗基锗烯(Me₂Ge=Ge:)与乙醛环加成反应的反应机制,奠定了亚锗基锗烯(H₂Ge=Ge:)及其衍生物(X₂Ge=Ge:, X=H, Me, F, Cl, Br, Ph, Ar?)与非对称性π键化合物环加成反应的理论基础.     

硅烯和锗烯的生长及其机制研究

正硅烯和锗烯分别是由硅原子和锗原子组成的具有类似石墨烯结构的二维材料。与组成石墨烯的sp~2杂化的碳原子不同,硅原子和锗原子在能量上更倾向于sp~3杂化,这是一种三维的共价键构型,所以在自然界中不存在类似石墨那样的层状结构的块体硅和锗,因此也不可能像剥离石墨烯那样从块体中得到硅烯和锗烯单层。这两种材料的生长需要使用单层可控的沉积技术,并选择合适的基底,从而使硅和锗倾向于二维平面生长而     

700℃退火下铝调制镍硅锗薄膜的外延生长机理

文章研究了在700℃退火下,铝插入层调制镍和硅锗合金反应形成单相镍硅锗化物的生长机理.透射电镜测试结果表明,镍硅锗薄膜和硅锗衬底基本达到赝晶生长;二次质谱仪和卢瑟福沟道背散射测试结果表明,在镍硅锗薄膜形成的过程中,铝原子大部分移动到镍硅锗薄膜的表面.研究结果表明,铝原子的存在延迟了镍和硅锗合金的反应,镍硅锗薄膜的热稳定性和均匀性都得到了提高.最后,基于上述实验结果给出了铝原子调制形成外延镍硅锗薄膜的生长机理.     

微尺度下硅锗合金热导率的分子动力学模拟

采用非平衡分子动力学(NEMD)方法研究了微尺度下硅锗合金的热导率变化情况.结果表明,硅锗合金热导率具有明显的尺寸效应,显著小于大体积晶体的实验值;并且受边界散射效应的影响,热导率值随硅锗原子百分比的不同发生变化;同时热导率随温度的升高而增大,与实验值比较大致吻合.     

SimGen(m+n=9)团簇结构和电子性质的计算研究

硅锗团簇结构与电子性质的研究对于研发新型微电子材料具有重要意义. 将遗传算法和基于密度泛函理论的紧束缚方法相结合, 研究了Si_mGe_n(m+n=9)团簇的原子堆积结构和电子性质. 计算结果发现, Si_mGe_n(m+n=9) 团簇存在两种低能原子堆积稳定构型: 带小金字塔的五边形双锥堆积和带桥位Ge原子的四面体紧密堆积. 随着团簇内锗原子数目的逐渐增加, 两种堆积结构均出现明显的转变, 其中最低能量的几何结构由单侧带相邻双金字塔的五边形双锥结构转变为双侧带相邻单金字塔的五边形双锥结构. 随着原子堆积结构的变化, 团簇内原子电荷分布及电子最高占据轨道与电子最低未占据轨道的能隙随团簇内所含硅和锗元素组分的不同呈现出明显的差异.     

微波消解石墨炉原子吸收光谱法测定蒙山全蝎中的痕量锗

建立了石墨炉原子吸收光谱法测定蒙山全蝎中痕量元素锗的方法.通过程序控温、控压的分步微波消解方式消解样品,优化石墨炉升温程序,采用Ni(NO3)2为基体改进剂,以氘灯扣除背景,在265.2nm波长下测定蒙山全蝎中痕量元素锗.在选定分析条件下,锗的检出限为0.30μg/L,RSD的范围为1.2%-3.1%,回收率为88.9...     

二氯亚锗基卡宾与甲醛生成锗杂双环化合物反应的从头算研究

用CCSD(T)//MP2/6-31G^*方法研究了单重态二氯亚锗基卡宾(Cl₂Ge=C:)与甲醛生成锗杂双环化合物的环加成反应机理,根据该反应的势能面可以预言,该反应有两条相互竞争的主反应通道．该反应所呈现的反应规律为：二氯亚锗基卡宾中C原子的2p空轨道因从氧端插入甲醛的π轨道而造成了中间体的形成;在中间体和两反应物之间,因二氯亚锗基卡宾和甲醛中的两成键π轨道发生了[2+2]环加成作用,从而分别生成了Ge-O对位的和Ge-O顺位的两四元环化合物;由于四元环化合物中卡宾C原子的不饱和性,进一步与甲醛作用,从而生成了两锗杂双环化合物．     

Robustness of quantum correlations against decoherence

We study dynamics of nonclassical correlations by exactly solving a model consisting of two atomic qubits with spontaneous emission. We find that the nonclassical correlations defined by different measures give different qualitative characterizations of those correlations. The relative behaviors of those correlation measures are presented explicitly for various quantum states in the two-qubit atomic system. In particular, we find that the robustness of quantum correlations can be greatly enhanced by performing appropriate local unitary operations on the initial state of the system.     

Velocity correlations and the structure of nonequilibrium hard-core fluids

A model for the pair-distribution function of nonequilibrium hard-core fluids is proposed based on a model for the effect of velocity correlations on the structure. Good agreement is found with molecular dynamics simulations of granular fluids and of sheared elastic hard spheres. It is argued that the incorporation of velocity correlations are crucial to correctly modeling atomic scale structure in nonequilibrium fluids.     

Quantum correlations among superradiant Bose-Einstein condensate atoms

Quantum correlations among atoms in superradiant Bose-Einstein condensates are discussed. It is shown that atoms in the superradiant atomic condensate can exhibit continuous variable quantum entanglement analogous to Einstein-Podolsky-Rosen (EPR)-type quantum correlations. Comparison to quantum entanglement in the Dicke model in thermal equilibrium is provided.     

辐射的相干性和熵的增加

本文讨论一个多原子辐射模型:N个有两能级的原子体系(A),与一个单模辐射(B)彼此耦合,A和B又分别同热库D和C耦合,假设在辐射场波长范围内所有原子有相同的相位,则在长波、旋转波和平均场近似下,用密度矩阵方法,引入Markov近似,便可导得A,B两体系的运动方程,这一组方程包含了单原子的自发辐射和热辐射引起的吸收、感应辐射,同时也包含了单模相干态辐射引起的N个原子的感应辐射以及这多原子体系的相干自发辐射过程。后两种过程实际上是始于Dicke模型而后曾被人们多次讨论过的两类超辐射过程,我们对上述五种过程进行 关键词：     

Transverse momentum distributions and their forward-backward correlations in the percolating color string approach

The forward-backward correlations in the p(T) distributions at midrapidity, which present a clear signature of nonlinear effects in particle production, are studied in the model of percolating color strings. Quantitative predictions are given for these correlations at SPS, RHIC, and LHC energies. Interaction of strings also naturally explains the flattening of p(T) distributions and increase of with energy and atomic number for nuclear collisions.     

Nature of correlations in the atomic limit of the boson fermion model

Using the equation of motion technique for Green's functions we derive the exact solution of the boson fermion model in the atomic limit. Both (fermion and boson) subsystems are characterised by the effective three level excitation spectra. We compute the spectral weights of these states and analyse them in detail with respect to all possible parameters. Although in the atomic limit there is no true phase transition, we notice that upon decreasing temperature some pairing correlations start to appear. Their intensity is found to be proportional to the depleted amount of the fermion nonbonding state. We notice that pairing correlations behave in a fashion observed for the optimally doped and underdoped high T_c superconductors. We try to identify which parameter of the boson fermion model can possibly correspond to the actual doping level. This study clarifies the origin of pairing correlations within the boson fermion model and may elucidate how to apply it for interpretation of experimental data. Received 31 January 2003 / Received in final form 18 March 2003 Published online 23 May 2003 RID="a" ID="a"e-mail: doman@kft.umcs.lublin.pl     

依赖强度耦合Jaynes-Cummings模型中原子和场的Disentangled-states及其演化特性

分析了依赖强度耦合Jaynes-Cummings模型在初始相干光场较强的情况下(1)原子和场退耦合的条件,详细地研究了对于不同的原子初态原子和场的各种disentangled-states的确切表达式及其演化的周期性,并且用密度算符间的距离对原子和场的这些disentangled-states及其演化进行了充分的论证. 关键词：     

Correlations in atomic systems: diagnosing coherent superpositions

While investigating quantum correlations in atomic systems, we note that single measurements contain information about these correlations. Using a simple model of measurement-analogous to the one used in quantum optics-we show how to extract higher-order correlation functions from individual "photographs" of the atomic sample. As a possible application, we apply the method to detect a subtle phase coherence in mesoscopic superpositions.     

The problem of determining short-range order parameters in interpreting a M?ssbauer spectrum

We develop a procedure to interpret the model M?ssbauer spectra (MS) of resonant nuclei in a two-component crystal with short-range order. The procedure is describable not only by pair correlations but also by multiparticle correlations of the atomic distribution. The results of the interpretation are used to find M?ssbauer parameters for subspectra and for certain correlation moments that describe the short-range order. The developed approach was used to interpret the actual spectra of ⁵⁷Fe in iron-chromium alloys.     

Nucleon Isovector Pairing in Nuclei: Microscopic Approach,Boson Representation,and Collective Model

Nucleon pair correlations in atomic nuclei are analyzed within a nuclear microscopic model with residual isovector pairing forces. These are formulated in the boson representation of fermion operators whereby the collective mode of pair excitations can be isolated without restricting the size of the one-particle basis. This method allows one to analyze the fluctuations in the nonsuperfluid phase of nuclear matter, its phase transition to the superfluid phase, and strong pair correlations. The performance of the method is exemplified by numerical results for the nuclei in the vicinity of the doubly magic ⁵⁶Ni nucleus.