Visualization of Metal-to-Ligand and Ligand-to-Ligand Charge Transfer in Metal-Ligand Complexes

利用三种方法可视化化了Ru(II) ammine的金属到配体的电荷转移. 首先原子分辨的态密度显示HOMO上的密度主要在Ru上,LUMO 上的态密度在ammine上,这说明Ru上激发的电子会转移到ammine配体上. 第二,电荷差异密度揭示了所有的空穴都在Ru上,所有的电子都在ammine上. 第三,跃迁密度矩阵揭示了Ru和ammine上的电子空穴对的相关性. 这三种方法也用来研究Os(bpy)₂(p0p)Cl的金属到配体的电荷转移和Alq3配体到配体的电荷转移.     

混合卤化物中的极化子与双极化子

应用紧束缚双带模型对混合卤化物的电荷掺杂性质进行了计算,发现单电荷掺杂在混合卤化物中形成极化子,双电荷掺杂则形成稳定的双极化子;单体的长度和界面耦合都对极化子和双极化子的产生和稳定性有影响.混合卤化物的单体对掺杂电荷具有选择性;电子-电子相互作用并不能使形成双极化子的两个同号电荷相互排斥而形成两个单极化子.在具有电荷自发转移的材料中,混合卤化物单体对掺杂电荷没有像其他混合卤化物一样的选择性,掺杂电荷的定域位置取决于两种单体对该电荷的束缚能力. 关键词： 混合卤化物 极化子 电荷约束     

过渡族金属化合物中的电荷密度波

绝大部分化合物都可以结晶成规则形状的晶体.在这些晶体里,除了缺陷、杂质和晶界以外,晶胞无限循环重复.但是,在足够低的温度下,一些化合物晶胞之间的电子-离子相互作用,使这种规则排列产生小小的崎变,变得不稳定起来.在稳定的状态中,电荷密度、自旋密度或离子位置为长周期调制,这些调制的周期可能与基本晶格的周期是无公度的.结果,晶体有了两个独立的周期,不再是真正周期性的了.本文将集中讨论电子密度以及离子位置都出现周期变化的电荷密度波. 一、一维电荷密度波 大约二十年前,R.Peierls和 H.Frohlich首先提出,电荷密度波能降低金属的…     

N2H4在NiFe(111)合金表面吸附稳定性和电子结构的第一性原理研究

采用基于色散校正的密度泛函理论进行了第一性原理研究, 详细分析了肼(N₂H₄)在Ni₈Fe₈/Ni(111)合金表面稳定吸附构型的吸附稳定性和电子结构及成键性质. 通过比较发现, 肼分子以桥接方式吸附在表面的两个Fe原子上是最稳定的吸附构型, 其吸附能为-1.578 eV/N₂H₄. 同时发现, 肼分子在这一表面上吸附稳定性的趋势为: 桥位比顶位吸附更有利, 且在Fe原子上比在Ni原子上的吸附作用更强. 进一步分析了不同吸附位点上稳定吸附构型的电子结构、电荷密度转移以及电子局域化情况. 结果发现: 相同吸附位点的电子态密度图基本一致, 并且N原子的p轨道和与之相互作用的表面原子的d轨道之间存在态密度上的重叠; 吸附后电荷密度则主要从肼分子转移到表面原子之上; 在电子局域化函数切面图中也发现吸附后电子被局域到肼分子的N原子和相邻的表面原子之间. 这些电子结构的表征都充分说明肼分子与表面原子之间通过电荷转移形成了强烈的配位共价作用.     

异质结电荷转移的密度矩阵理论近似研究

分子半导体组成的异质结构是染料敏化太阳能电池的主要部分,电荷转移效率的提高是太阳能转换效率的关键.在金属纳米粒子与染料分子和半导体TiO2组成的系统中,考虑半导体的晶格结构、电子波函数在晶格边界的反射及金属纳米粒子中的等离激元效应,应用密度矩阵理论研究在光激发分子作用下电荷从分子转移到半导体晶格的动力学过程,采用密度矩阵和波函数相结合的处理方案研究了分子半导体电荷转移过程中的等离激元效应.研究发现金属钠米粒子激发所产生的等离激元可以使电荷从分子到半导体的转移效率提高3个数量级,是提高电荷转移效率的有效手段,且密度矩阵理论与波函数相结合的方法使得计算分子与15 nm尺度的半导体纳米晶体间的电荷转移成为可能,理论分析了表面等离激元的增益作用对电荷转移的影响.     

原子氢在Be(100)薄膜上吸附的第一性原理计算

对原子氢在Be(1010)薄膜表面的吸附性质做了第一性原理计算研究.根据原子面间距的不同,可把Be(1010)表面分为两种.计算结果表明,原子氢在这两种表面上的吸附性质显著不同.为阐明和分析这些不同,系统计算和分析了Be(1010)薄膜的表面电子结构、电子功函数、平均静电势和局域电荷密度.这些物理量都自洽地表明,吸附过程中原子氢和表面铍原子间的电荷转移过程对于两种表面是完全不同的.对于L型表面来说,电荷由吸附原子氢向表面Be原子层转移,而对于S型表面而言,电荷转移过程恰恰相反.     

C60富勒烯-巴比妥酸及其二聚体几何结构和电子结构的密度泛函计算研究

采用基于密度泛函理论的广义梯度近似,对C₆₀富勒烯-巴比妥酸及其二聚体的几何结构和电子结构进行了计算研究.发现：C₆₀富勒烯-巴比妥酸只有一种稳定结构,且掺杂巴比妥酸基团对C₆₀分子构型的影响是局域的.C₆₀富勒烯-巴比妥酸的二聚体有三种同素异构体,分别以［6,5］—［6,5］,［6,6］—［6,5］和［6,6］—［6,6］三种方式键合,从能隙大小顺序和总能相对大小来看,［6,6］—［6,6］结构最为稳定.电子结构方面,在C₆₀富勒烯-巴比妥酸单体中,Donor-Acceptor电荷转移体系为C₆₀富勒烯-巴比妥酸,即电荷是从C₆₀向巴比妥酸转移.由前线轨道和自旋布居数得知,C₆₀富勒烯-巴比妥酸单体很好地保留了C₆₀的电磁性质,但稳定性下降,易发生二次加成反应形成二聚体.对于C₆₀富勒烯-巴比妥酸二聚体,Mulliken电荷分析显示,在加成四元环处的碳原子分别得到0104e和0106e电荷,而与它们邻近的碳原子则失去电子,带有正电荷,且距加成位置越近的碳原子失去的电荷越多.在远离加成位置处,碳原子的净电荷变化相对较小.与单体152eV能隙相比,二聚体中的能隙为1.45eV.其前线轨道分布与单体相比,最高占据轨道几乎未变,但最低未占据轨道发生了很大变化. 关键词： 几何结构 电子结构 密度泛函     

FeV(O)(TAML)高价铁-氧反应中间体活化C-H键的机理转变的理论研究

本文运用密度泛函理论对Gupta实验中脂肪族与芳香族底物C-H键氧化反应中所表现出的动力学差异进行深入的机理研究. 计算表明,这种差异是由于两种底物(脂肪族的环己烷、2,3-二甲基丁烷两种底物以及芳香族的甲苯、乙苯和异丙苯三种底物)C-H键活化反应机理的不同所造成. 对于脂肪族底物,活性反应中间体Fe^V(O)(TAML)进行C-H氧化是一种氢原子转移过程;而对于芳香族底物,C-H键活化则是一个质子耦合的电子转移过程,并且在过渡态具有质子转移特性,即质子耦合的电子转移过程. 这种差异是由四氨基的TAML环和芳香底物的苯环之间存在的π-π相互作用产生的,具有“拉电子”效应,从而使得电子从芳香化底物转移到Fe^V(O)(TAML)氧化物的效率降低.     

δ-Pu空位缺陷的密度泛函理论计算

采用密度泛函理论框架下的平面波赝势方法,计算了空位缺陷对δ-Pu结构稳定性和电子结构的影响.建立了1×1×2、2×2×1和2×2×2 3种晶胞中的空位缺陷模型,分别计算了其晶格常数、空位形成能、结合能、态密度、电荷密度分布以及Mulliken电荷布居.计算结果表明:空位缺陷在δ-Pu中不能稳定存在,且会导致晶体的整体结构稳定性降低.在3种缺陷模型中,2×2×1的模型空位稳定性和结构稳定性都相对更强;空位导致δ-Pu电子的局域性降低,电子相互作用也发生了一定的变化,其中2×2×1的模型中与空位最邻近的Pu原子发生了明显的sp杂化,这在一定程度上说明了其稳定性最强的原因;空位引起电荷由近空位端向近Pu端转移,且导致最邻近Pu原子失去电子,而这部分电子主要由6p轨道贡献.     

三甲基苯基六氟磷酸铵离子液体结构性质的密度泛函研究

离子液体以其独特性质广受关注，人们对其潜在的利用价值做了大量的研究.本文采用密度泛函（DFT）B3LYP/6-31(d)的方法计算了三甲基苯基六氟磷酸铵离子液体的几何和电子结构，对比对了三种不同的优化结构.通过自然键轨道(NBO)分析，得到各原子的电荷分布，并用二阶微扰稳定化能分析了阴阳离子间相互作用.结果发现：阴离子分布在阳离子周围的三个区域，所有离子对中阴阳离子间有电荷的转移，且都存在多重氢键作用，阴阳离子间的电荷转移主要是通过LPF→σ*C-H 相互作用.     

Experimental and Theoretical Studies on the Interaction between Isonicotinic Acid Molecules and Silver Nanoclusters

The present paper describes the studies on the adsorption behavior and charge transfer from isonicotinic acid to silver nanoparticles with experiment and theory. Compared with UV–Visible adsorption spectrum, the adsorption spectrum of Ih-Ag₁₃ cluster was quite good agreed with that of silver colloidal nanoparticle. So that one Ag₁₃ cluster as a substrate was used to simulate Raman frequencies of the adsorption configuration. Here, it is demonstrated the calculated Raman spectra are in good agreement with experimental results. The analysis of Mulliken charge was obtained by density functional theory, which indicated the charge characteristics of Ag₁₃ nanoparticle. Once isonicotinic acid molecules were adsorbed on sliver clusters, the charges transfer from isonicotinic acid to silver clusters, so that the surface charges of silver clusters are uneven.     

What can the geometry tell about the charge distribution in the mesoionic heterocycles? A DFT study on the SCN4R2 system

This computational organic chemistry study was performed using the hybrid functional B3LYP. Many basis sets were evaluated and the basis set 6‐31G(d) was found to be the most practical in terms of time and accuracy. The study presents the first method in the chemical literature that allows estimation of submolecular charges in mesoionic compounds. The theory was built on a reference model structure for which the absolute value of charge of the aromatic p‐orbitals is known. This is the cornerstone, and by employing the harmonic oscillator model of aromaticity (HOMA) many parameters can be quantified. The electronic structure of the title compound was the subject of this approach. The study addressed the following points: geometries, infrared frequencies, NMR chemical shifts, calculated charges, a chemical reactivity, and the frontier orbitals. The calculations illustrate that the π‐system of the CN₄ segment includes considerable aromatic character and carries a positive charge while the overall charge is negative. This allows classifying it as a σ‐acceptor/π‐donor while the exocyclic counter anion, the sulfur atom, is a σ‐donor/π‐acceptor. The substituents (R groups) in this case are only σ‐donors. The approach may be applied to other mesoionic and mesoaromatic systems. Copyright © 2009 John Wiley & Sons, Ltd.     

固液混合装药热传导特性对其安全性影响的计算研究

固液混合装药物理参数是影响装药安全性的主要因素之一,利用混合炸药计算物理参数的方法,计算了几种典型配比装药的物理参数,根据能量守恒方程对不同物理参数的装药进行数值模拟。计算得到:在温度载荷相同的条件下,不同的物理参数对其温度响应有较大的差别,说明分析固液混合装药安全性时,应考虑装药不同比例对其安全性的影响,才能真实反应热点能量演化过程,为分析固液混合装药的安全性提供一定的理论依据。     

EICO measurements of inner-core excited mixed rare-gas clusters

The spectra of deep inner-core excited mixed rare-gas clusters were recorded by using electron ion coincidence (EICO) and multi-hit momentum imaging (MHMI) techniques. The EICO spectra for Ar₉₉Kr₁ clusters reveal that singly charged ions are emitted from the inner-core excited clusters in addition to the multiple charged ions. The dependence of the EICO spectra on photon energy and cluster size suggests that the holes created through vacancy cascade on the krypton atoms are transferred to the surrounding atoms, and that the singly charged ions are the primary product of the krypton photoabsorption. Charge localization is suggested for the inner-core excited mixed rare-gas clusters from the analysis of the EICO peak width. The MHMI measurements give us direct evidence for the strong charge migration from X-ray absorbing atoms to surrounding atoms. The photon energy dependence of the PSD image for fragment ions suggests that the momentum of the fragment ions depends on the number of charges generated by the vacancy cascade.     

On the encapsulation of azafullerenes inside the single-walled carbon nanotubes: Density-functional theory based treatments

We theoretically studied the encapsulation of azafullerene (C₅₉N) inside the single-walled carbon nanotubes (SWCNTs) from the first-principles. Adsorption energy is calculated, and the azafullerene affinities for the typical semiconducting and metallic nanotubes are investigated and compared with those of pure C₆₀ fullerene. It has been found that the azafullerene as well as the fullerene affinity for the semiconducting nanotubes is stronger than that for the metallic ones, and the energy values and binding distances are typical for the physisorption. Our first-principles results indicate that the interaction between SWCNTs and azafullerenes is comparable with the nanotubes-C₆₀ system. The charge analysis shows, however, that the charges have been transferred from the cage to the tube in the azafullerene peapods, while in the fullerene peapods the charges were found to be transferred from the tube to the fullerene nanocage. Furthermore, it was found that the interaction between the considered fullerenes and host nanotubes strongly depends on the tube diameters.     

Numerical simulation of particle size effects on contact electrification in granular systems

Based on the contact charge transfer model between two particles due to a single collision proposed by Apodaca, the contact charges carried on a particle is derived due to multiple collisions, including the repeat collisions between two particles and the collisions with different particles, in mixed-size granular system of identical material. The effect of the particle size on the charges carried on the particle is simulated. The results indicate that for a mixed-size granular system, due to multiple collisions among particles, there exists a threshold particle radius, the particles with radius higher than which and the particles with radius lower than which carry opposite charges. The threshold particle radius is equal to mean value of particle size in the mixed-size granular system. Basically, the polarity of the charges carried on the largest particle is same as the polarity of the transfer charge carrier, and in case of the positive charge transferred, the largest particle will be positively charged and the smallest particle will be negatively charged, and vice versa. In the same size region, the more dispersive the particle size is, the more the net charges can be produced. In normal-distributed granular system, the magnitude of contact charge is determined mainly by the particle size distribution, size region, total particle number and the relative impact velocity.     

Composite optical vortices in noncollinear Laguerre--Gaussian beams and their propagation in free space

Taking two Laguerre-Gaussian beams with topological charge 1 = ±1 as an example, this paper studies the composite optical vortices formed by two noncollinear Laguerre-Gaussian beams with different phases, amplitudes, waist widths, off-axis distances, and their propagation in free space. It is shown by detailed numerical illustrative examples that the number and location of composite vortices at the waist plane are variable by varying the relative phase β, amplitude ratio η, waist width ratio ξ, or off-axis distance ratio μ. The net topological charge lnet is not always equal to the sum lsum of charges of the two component beams. The motion, creation and annihilation of composite vortices take place in the free-space propagation, and the net charge during the propagation remains unchanged and equals to the net charge at the waist plane.     

Different mechanism of capacitance change for gas detection using semiconducting and metallic single-walled carbon nanotubes

Semiconducting single-walled carbon nanotubes (s-SWCNTs) with lower absorption energy of NO₂ gas exhibited higher sensitivity than metallic SWCNTs. The result originated from quantum capacitance of s-SWCNTs, which was readily affected by charge transfer, whereas that of m-SWCNTs showed no change with even more transferred charges. However, m-SWCNT that were aligned polarize adsorbed gases on the surface by a local field that contributed the capacitance changes of m-SWCNT networks. This is a newly introduced detection mechanism of gas sensing using m-SWCNTs.     

氟聚合物压电驻极体的压电性及其电荷的动态行为

描述了一种可控微结构的多孔聚合物压电功能膜的制备方法,讨论了采用该工艺制备的聚四氟乙烯(PTFE)和全氟乙丙烯共聚物(FEP)复合膜压电驻极体的压电性能及其热稳定性.通过等温压电系数衰减和短路热刺激放电(TSD)方法,研究了氟聚合物复合膜压电活性热稳定性改善的根源,以及脱阱电荷输运和复合的特性.结果表明,这类氟聚合物压电驻极体膜的准静态压电系数d₃₃可高达2200pC/N;压电系数d₃₃的压强特性在直到20kPa的压强范围内呈现良好的 关键词： 氟聚合物 压电驻极体 热稳定性 电荷动态特性     

掺杂PVK薄膜的荧光谱及电荷转移

根据PVK掺杂后荧光谱的变化，说明掺杂PVK薄膜的电致发光存在着从基质分子向掺杂分子的能量传递，用一个由单链模型扩展到包括杂质的哈密顿量进行数值求解，结果表明：在PVK和杂质分子之间有效的能量传递是源于它僮之间的电荷转移，且随着杂质浓度的变化，其荧光谱峰位的移动与掺杂前后系统总能量的改变及荧光谱强度与掺杂后转移的电荷数之间分别存在对应关系。该模型较好地解释了有关的实验结果。