H,Cl和F原子钝化Cu_2ZnSnS_4(112)表面态的第一性原理计算

采用基于密度泛函理论的第一性原理计算方法系统研究了Cu_2ZnSnS_4体相的晶格结构、能带、态密度及表面重构与H,Cl和F原子在Cu_2ZnSnS_4(112)表面上的吸附和钝化机理.计算结果表明:表面重构出现在以金属原子Cu-Zn-Sn终止的Cu_2ZnSnS_4(112)表面上,并且表面重构使表面发生自钝化;当单个H,Cl或F原子吸附在S原子终止的Cu_2ZnSnS_4(112)表面上时,相比于桥位(bridge)、六方密排(hcp)位和面心立方(fcc)位点,三种原子均在特定的顶位(top)吸附位点表现出最佳稳定性.当覆盖度为0.5 ML时,无论H,Cl还是F原子占据Cu_2ZnSnS_4(112)表面的2个顶位均具有最低的吸附能.以S原子终止的Cu_2ZnSnS_4(112)表面在费米能级附近的电子态主要由价带顶部Cu-3d轨道和S-3p轨道电子贡献,此即表面态.当H,Cl或F原子在表面的覆盖度达0.5 ML时,费米能级附近的表面态降低,其中H原子钝化表面态的效果最佳,Cl原子的效果次之,F原子的效果最差.表面态降低的主要原因在于吸附原子从S原子获得电子致使表面Cu原子和S原子在费米能级处的态密度峰几乎完全消失.     

Lowest Π–Π* electronic transitions in linear and two-dimensional polycyclic aromatic hydrocarbons: enhanced electron density edge effect

Polycyclic aromatic hydrocarbons (PAHs) form an important class of molecules as they are ubiquitous, pollute air and cause severe health problems. Lowest vertical π–π* singlet–singlet or triplet–triplet excitation energies and corresponding oscillator strengths were studied for several linear and two-dimensional PAHs employing time-dependent density functional theory. Excited-state electron density, molecular electrostatic potential (MEP) and spin density distributions in the PAHs, along with ground-state chemical hardness, were also studied. It has been found that, generally, excitation energies and oscillator strengths decrease with increase in PAH size, and excitation energies and chemical hardness are strongly linearly correlated. Enhanced electron density edge effect, which was found to occur in the ground states of the molecules, continues to hold in their excited states also. A strong similarity between the ground and π–π* excited-state MEP maps suggests that σ electrons are the main contributors to the enhanced electron density at the edges. Due to their strong electronic absorption transitions in the visible and infrared regions, the PAHs can be used for harnessing solar energy efficiently.     

Engineering the work function of armchair graphene nanoribbons using strain and functional species: a first principles study

First principles density functional theory calculations were performed to study the effects of strain, edge passivation, and surface functional species on the structural and electronic properties of armchair graphene nanoribbons (AGNRs), with a particular focus on the work function. The work function was found to increase with uniaxial tensile strain and decrease with compression. The variation of the work function under strain is primarily due to the shift of the Fermi energy with strain. In addition, the relationship between the work function variation and the core level shift with strain is discussed. Distinct trends of the core level shift under tensile and compressive strain were discovered. For AGNRs with the edge carbon atoms passivated by oxygen, the work function is higher than for nanoribbons with the edge passivated by hydrogen under a moderate strain. The difference between the work functions in these two edge passivations is enlarged (reduced) under a sufficient tensile (compressive) strain. This has been correlated to a direct-indirect bandgap transition for tensile strains of about 4% and to a structural transformation for large compressive strains at about - 12%. Furthermore, the effect of the surface species decoration, such as H, F, or OH with different covering density, was investigated. It was found that the work function varies with the type and coverage of surface functional species. Decoration with F and OH increases the work function while H decreases it. The surface functional species were decorated on either one side or both sides of AGNRs. The difference in the work functions between one-sided and two-sided decorations was found to be relatively small, which may suggest an introduced surface dipole plays a minor role.     

碳纳米管吸附铜原子的密度泛函理论研究

采用密度泛函方法对铜原子在有限长（5,5）椅型单壁碳纳米管的吸附行为进行了研究.计算结果表明,铜原子吸附在管外壁要比吸附在管内壁能量上更为有利,在管外壁碳原子顶位吸附最佳,属于明显的化学吸附.且用前线轨道理论对其成键特性进行了分析,表明在顶位吸附时主要由铜原子的4s轨道电子与碳纳米管中耦合的σ-π键形成新的σ键.此外还对比计算了两种典型位置电子密度,发现顶位吸附的成键中有更大的电子云重叠.进一步表明在某些情况下铜碳原子可以成键. 关键词： 碳纳米管 铜原子 成键特性     

An ab initio study on competition between pnicogen and chalcogen bond interactions in binary XHS:PH2X complexes (X = F,Cl, CCH,COH, CH3, OH,OCH3 and NH2)

Chalcogen and pnicogen bond interactions are studied in the binary XHS:PH₂X complexes (X = F, Cl, CCH, COH, CH₃, OH, OCH₃ and NH₂) using quantum chemical calculations. These interactions can be explained in terms of electrostatic effects, considering the chalcogen or pnicogen as a Lewis acid due to the presence of an σ-hole. Almost a perfect linear relationship is found between the interaction energies and the magnitudes of the product of most positive and negative electrostatic potentials. This reveals that both the negative and positive regions of the interacting atoms can be used to predict the strength of the eventual interaction. The nature of chalcogen and pnicogen bond interactions is unveiled by means of the atoms in molecules and electron localisation function analyses.     

Computational study of non-covalent interactions in oxirane…XF complexes (X = H,F, Cl,Br, Li) and their F-/Li-substituted analogues

A computational study found oxirane^…XF (X = H, Cl, Br, F, Li) dimers to be energetically stable, with their interaction energies increasing with the magnitude of the XF dipole moment in the order XF = LiF > BrF ～ HF > ClF > F₂. Their relative stabilities roughly correlate with the amount of charge transferred from the lone pairs on the O atom of oxirane to the antibonding σ* orbital of XF. However, the most strongly bound dimer, oxirane^…LiF, is stabilised by the largest dipole but involves the smallest charge transfer. The variation in the strength of the oxirane^…XF interaction was subsequently investigated by the sequential substitution of the protons on oxirane by either electron-donating Li or electron-withdrawing F atoms.     

无序碳单层的电子结构及氢原子吸附的第一性原理

本研究运用第一性原理计算方法,系统地研究了无序碳单层材料不同位点的电子结构及其析氢性能.计算结果显示无序结构中的C-C键相比于石墨烯中的C-C键在26.7%的范围内有不同程度的拉伸或压缩,使得C原子电荷在-0.17～+0.16个电子范围内变化,导致部分C原子电子局域化.电子的局域化增强了C原子的化学活性,从而表现出了较强的吸附性能.我们发现H原子与C原子的键合及析氢性能与C原子间的键角相关.对于三配位的碳原子,其中三个价电子通过sp~2杂化轨道与最邻近的碳原子结合形成较强的共价键,而余下的一个p_z轨道电子可以与H原子在垂直于原子层的方向形成较弱的化学键.无序结构可以打破三个sp~2杂化轨道的对称性,进而影响p_z轨道与氢的成键.本研究在一定程度上揭示了单层无序碳材料结构-性能的构效关系,为实验上设计特定性能的无序碳功能材料提供理论指导.     

远红外光纤材料(MnF2)x(BaCl2)100-x玻璃结构的EXAFS和WAXS研究

本文用扩展X射线吸收谱(EXAFS)和X射线大角散射谱(WAXS)对远红外光纤材料复合卤化物玻璃(MnF₂)_x(BaCl₂)_166-x(x=65,60,55)的短程结构进行了研究。从MnK吸收限的EXAFS和样品的非晶衍射图,得到了Mn原子的近邻原子配位信息。结果表明F,Cl原子在Mn原子周围形成了混合配位的八面体(MnCl₂F₄),这些八面体以Mn—F键为桥键连成“之”字型 关键词：     

Quantum-Chemical Study of Structural Stone–Wales Defect in Functionalized Fullerene C<Subscript>20</Subscript>

The formation energy and the Stone—Wales defect structure in fullerene C₂₀ doped with one of functional groups H, Cl, F, or OH are calculated within the density functional theory. It is shown that the functional group type and binding site have a significant effect on the defect formation energy. It is found that the C₂₀F compound is significantly more stable than other considered systems, i.e., C₂₀Cl, C₂₀H, and C₂₀OH.     

AIM Study on the Reaction of CH2SH Radical with Fluorine Atom

采用MP2(Full)/6-311G(d,p)、QCISD(T)/6-311++G(2df,p)和B3LYP/6-311G(d,p)方法研究了CH2SH自由基与F原子的反应．F原子通过进攻自由基上的C原子或S原子形成三种不同的反应通道．计算结果表明F原子进攻自由基上的C原子生成CH2S和HF为主要的反应通道．对反应进程中若干关键点进行了电子密度拓扑分析,找到了该反应的结构过渡区(结构过渡态)和能量过渡态．计算结果表明,对于比较显著的吸热或放热反应,其结构过渡区范围很小,对于吸热或放热不太显著的反应,结构过渡区范围较大.     

Quantum Monte Carlo investigations of adsorption energetics on graphene

We have performed calculations of adsorption energetics on the graphene surface using the state-of-the-art diffusion quantum Monte Carlo method. Two types of configurations are considered in this work: the adsorption of a single O, F, or H atom on the graphene surface and the H-saturated graphene system (graphane). The adsorption energies are compared with those obtained from density functional theory with various exchange-correlation functionals. The results indicate that the approximate exchange-correlation functionals significantly overestimate the binding of O and F atoms on graphene, although the preferred adsorption sites are consistent. The energy errors are much less for atomic hydrogen adsorbed on the surface. We also find that a single O or H atom on graphene has a higher energy than in the molecular state, while the adsorption of a single F atom is preferred over the gas phase. In addition, the energetics of graphane is reported. The calculated equilibrium lattice constant turns out to be larger than that of graphene, at variance with a recent experimental suggestion.     

DFT calculations for Au adsorption onto a reduced TiO2 (110) surface with the coexistence of Cl

Residual chlorines, which originate from HAuCl₄, enhance the aggregation of gold (Au) nanoparticles and clusters, preventing the generation of highly active supported Au catalysts. However, the detailed mechanism of residual-chlorine-promoted aggregation of Au is unknown. Herein to investigate this mechanism, density functional theory (DFT) calculations of Au and Cl adsorption onto a reduced rutile TiO₂ (110) surface were performed using a generalised gradient approximation Perdew, Burke, and Ernzerhof formula (GGA–PBE) functional and plane-wave basis. Although both Au and Cl atoms prefer to mono-absorb onto oxygen defect sites, Cl atoms have a stronger absorption onto a reduced TiO₂ (110) surface, abbreviated as rTiO₂ (110) in the following, than Au atoms. Additionally, co-adsorption of a Cl atom and a Au atom or Au nanorod onto a rTiO₂ surface was investigated; Cl adsorption onto an oxygen defect site weakens the interaction between a Au atom or Au nanorod and rTiO₂ (110) surface. The calculation results suggest that the depletion of interaction between Au and rTiO₂ surface is due to strong interaction between Cl atoms at oxygen defect sites and neighbouring bridging oxygen (O^B) atoms.     

Substituent effects on gas-phase acidities of formic acid and its silicon and sulphur derivatives R − M(= X)XH(M = C., Si; X = O,S; R = H,F, CI,OH, NH2 and CH3)

Ab initio molecular orbital methods at the CBS-Q level of theory have been used to study the effect of substituent (F, Cl, NH₂, OH and CH₃) on the gas-phase acidities of formic acid, HCOOH, its silicon and sulphur derivatives R-M(= X)XH(M = C., Si; X = 0, S; R = F, Cl, OH, NH₂ and CH₃). For formic acid and its thio and dithio derivatives the acidity changes upon substitution are irregular and depend on both the type of substituent, position and degree of replacement of oxygen atoms by sulphur atoms. For sila carboxylic acids and their thio and dithio derivatives the calculated acidities regularly increase in the order: R-SiOOH < R-Si(=S)OH ? R-Si(=O)SH < R-SiSSH(R = H, F, Cl, OH, NH₂ and CH₃). The chloro derivatives are the strongest among the acids studied. The highest gas phase acidity (1277.6 kJmol^?1) has been calculated for ClC(=S)OH.     

MEAM study of carbon atom interaction with Ni nano particle

Carbon, Ni, and C-Ni alloy modified embedded atom method (MEAM) potentials were developed to study the initial process of carbon nanotube growth on Ni catalyst particles. The MEAM potentials were used to study the atomistic interaction between a carbon atom and a fcc Ni nano particle, both on the particle surfaces and inside the Ni nano particles. The result shows that surface carbon atom is more stable than those in the bulk and sub-surface interstitial positions. Carbon atoms are expected to diffuse from the bulk to the surface, and the single walled and double-walled carbon nanotubes would be more favorable to form on Ni nano particle catalyst. The carbon and Ni nano particle interaction calculation shows that the corner and the edge of the particle are the energetically more favorable sites for the carbon adatom. The carbon nanotube may grow from the corner and edge of the particle.     

Effect of substitution and cooperativity on the Cl–F blue shift in single-electron halogen-bonded H3C ··· ClF complex

The effect of substitution and cooperativity on the blue shift of Cl–F stretch vibration in H₃C ··· ClF complex has been studied with quantum chemical calculations at the UMP2(Full)/aug-cc-pVTZ level. The electron-withdrawing group (F atom) in the electron donor decreases the blue shift, whereas the electron-donating group (methyl group) in the electron donor cause it to increase. The cooperativity between two different types of halogen bonds in H₃C ··· ClF ··· ClF complex enhances the strength of single-electron halogen bond and the blue shift. The natural bond orbital (NBO) and atoms in molecules (AIM) analyses have been performed for the halogen-bonded complexes.     

Dangling bond modulating the electronic and magnetic properties of zigzag SiGe nanoribbon

First-principles nonmagnetic calculations reveal a metallic character in zigzag SiGe nanoribbons (ZSiGeNRs) regardless of their width. The partial DOS projected onto the Si and Ge atoms of ZSiGeNR shows that a sharp peak at the Fermi level is derived from the edge Si and Ge atoms. The charge density contours show the Si–Ge bond is covalent bond, while for the Si–H bond and Ge–H bond, the valence charges are strongly accumulated around H atoms due to their stronger 1 s potential and the higher electronegativity of 2.20 than that of 1.90 for Si atom and 2.01 for Ge atom, so that a significant charge transformation from Si or Ge atoms to H atoms and thus an ionic binding feature. Spin–polarization calculations show that the band structures of ZSiGeNR are modified by the dangling bonds. Compared with perfect ZSiGeNR which is a ferrimagnetic semiconductor, the bands of the ZSiGeNRs with bare Si edge, bare Ge edge, and bare Si and Ge edges shift up and nearly flat extra bands appear at the Fermi level. The ZSiGeNR with bare Si edge or bare Ge edge is a ferrimagnetic metal, while ZSiGeNR with bare Si and Ge edges is a nonmagnetic metal.     

Carbene–aerogen bonds: an ab initio study

Through the use of ab initio calculations, the possibility of formation of σ-hole interaction between ZO₃ (Z = Ar, Kr and Xe) and carbene species is investigated. Since singlet carbenes show a negative electrostatic potential on their divalent carbon atom, they can favourably interact with the positive electrostatic potential generated by the σ-hole of Z atom of ZO₃. The characteristic of this interaction, termed as ‘carbene–aerogen’ bond, is analysed in terms of geometric, interaction energies and electronic features. The energy decomposition analysis indicates that for all complexes analysed here, the electrostatic energy is more negative than the polarisation or dispersion energy term. According to the electron density analysis, some partial covalent character can be ascribed to Xe???C interactions. In addition, the carbene–aerogen bond exhibits cooperative effects with the H???O hydrogen-bonding interaction in ternary complexes where both interactions coexist. For a given carbene, the amount of these cooperative effects increases with the size of the Z atom. The results obtained in this work may be helpful for the extension and future application of σ-hole intermolecular interactions as well as coordination chemistry.     

Dimers and trimers of polycyclic aromatic hydrocarbons as models of graphene bilayers and trilayers: enhanced electron density at the edges

Structures of dimers and trimers of polycyclic aromatic hydrocarbons (PAHs) having zig-zag edges, and continuous electron density and molecular electrostatic potential (MEP) distributions in these systems were studied in gas phase. Dimers of benzene and naphthalene for which high-accuracy results are available were used to test the reliability of four different functionals of density functional theory in combination with the 6-31G(d,p) basis set. The dispersion-corrected WB97XD functional was found to be distinctly superior to the other three functionals used and was employed to study PAH dimers and trimers. Electronic structures and geometries of dimers of a four benzene ring and a nine benzene ring systems and trimers of the four benzene ring system were investigated. The dimers and trimers of PAHs were found to be of parallel-displaced type, as observed experimentally for graphene. The enhanced electron density edge effect found in the PAH monomers earlier is found to exist in the dimers and trimers also.     

Cl原子在γ-TiAl(111)表面吸附的第一性原理研究

基于密度泛函理论,在广义梯度近似下研究了Cl在γ-TiAl(111)表面的吸附.计算结果表明:γ-TiAl(111)表面的面心立方位置(fcc)和六角密排位置(hcp)为Cl吸附的稳定位置,当覆盖度Θ小于一个单层(ML)时,Cl原子倾向于吸附在γ-TiAl(111)表面近邻为多Ti的位置.电子结构分析发现,Cl原子同表面金属原子形成较强的离子键,并且成键具有一定的方向性.当Cl原子和O原子共同在γ-TiAl(111)表面吸附时,二者都趋     

A reaction cell for time‐resolved in situ XAS studies during wet chemical synthesis: the Cu2(OH)3Cl case

The use of in situ time‐resolved dispersive X‐ray absorption spectroscopy (DXAS) to monitor the formation of Cu₂(OH)₃Cl particles in an aqueous solution is reported. The measurements were performed using a dedicated reaction cell, which enabled the evolution of the Cu K‐edge X‐ray absorption near‐edge spectroscopy to be followed during mild chemical synthesis. The formed Cu₂(OH)₃Cl particles were also characterized by synchrotron‐radiation‐excited X‐ray photoelectron spectroscopy, X‐ray diffraction and scanning electron microscopy. The influence of polyvinylpyrrolidone (PVP) on the electronic and structural properties of the formed particles was investigated. The results indicate clearly the formation of Cu₂(OH)₃Cl, with or without the use of PVP, which presents very similar crystalline structures in the long‐range order. However, depending on the reaction, dramatic differences were observed by in situ DXAS in the vicinities of the Cu atoms.