卤素驱动石墨二炔带隙的打开以实现光催化全解水（英文）

本文通过杂化密度泛函理论研究了卤素(F、Cl和Br)功能化的石墨二炔的能带结构.结果表明修饰的石墨二炔的带隙能随着卤素原子对的增加而增加;同时,价带顶的位置受卤素原子电负性大小的影响;当石墨二炔表面的卤素原子数目相同时,卤素原子的电负性越大,改性后石墨二炔的价带顶的位置越深.另外,计算结果表明石墨二炔的带隙可以通过不同卤素原子的适当混合修饰来有效调节,不同卤素原子混合修饰的石墨二炔的价带底和导带顶跨越了水的氧化还原电位.通过热力学分析进一步证明,不同卤素原子混合修饰的石墨二炔比单一卤素修饰的石墨二炔表现出更好的光催化水全解反应活性.这项工作对于如何设计更高效的全解水光催化剂提供了洞见.     

氢、氟原子边缘修饰β-GeSe纳米带的第一性原理研究

采用第一性原理计算方法研究了二维β相GeSe的电子结构,通过对二维单层β-GeSe剪切得到一维β-GeSe扶手椅型纳米带.研究不同带宽(N=1-5)β-GeSe扶手椅型纳米带的几何结构和电子性质,发现不同带宽纳米带能带带隙不同,带隙总体上随着带宽减小,而纳米带直接带隙半导体性质不受带宽影响.通过使用H、F原子对GeSe扶手椅型纳米带边缘修饰,H原子修饰纳米带导致能带类型从直接带隙向间接带隙的转变.在费米能级附近处F原子各轨道对价带和导带贡献比H原子各轨道贡献多,在边缘修饰中纳米带对F原子更加敏感.未修饰和使用H原子修饰纳米带在可见光范围内没有吸收峰,用F原子修饰纳米带在可见光范围内出现吸收峰.研究表明可以通过边缘修饰调控纳米带光学特性.     

γ石墨炔衍生物结构稳定性和电子结构的第一性原理研究

通过基于密度泛函理论的第一原理计算,系统研究了γ石墨炔衍生物的结构稳定性、原子构型和电子性质.γ石墨炔衍生物的结构是由碳六元环以及连接六元环间的碳链组成,碳链上的碳原子数为N=1—6.研究结果表明,碳链上碳原子数的奇偶性对γ石墨炔衍生物的结构稳定和相应的原子构型、电子结构性质具有很大的影响.其奇偶性规律为:当六元环间的碳原子数为奇数时,体系中的碳链均为双键排布,系统呈现金属性;当六元环间的碳原子数为偶数时,系统中的碳链形式为单、三键交替排列,体系为直接带隙的半导体.直接带隙的存在能够促进光电能的高效转换,预示着石墨炔在光电子器件中的应用优势.N=2,4,6的带隙分布在0.94—0.84 eV之间,带隙的大小与碳链上三键的数量和长度有关.研究表明,将碳原子链引入到石墨烯碳六元环之间,通过控制引入的碳原子个数可以调控其金属和半导体电子特性,为设计和制备基于碳原子的可调控s-p杂化的二维材料和纳米电子器件提供了理论依据.     

石墨炔管能带和力学性质的第一性原理研究

基于第一性原理计算,这篇文章研究了单壁锯齿型和扶手型石墨炔管的几何结构、电子结构以及杨氏模量.计算表明:石墨炔管是一类具有一定能隙的直接带隙半导体管,其带隙在0.4-1.3eV的能量范围,且随管径的增大而变小.而石墨炔管的杨氏模量在0.44-0.50Tpa区间变化.对于锯齿型石墨炔管,其杨氏模量随着半径的增大而变小而锯齿型石墨炔管的杨氏模量随其半径的增大而增大.     

β石墨炔衍生物结构稳定性及电子结构的密度泛函理论研究

石墨炔衍生物比石墨烯具有更多样化的原子结构,因而具有潜在的更丰富的电子结构.通过第一性原理密度泛函理论研究方法系统研究了β石墨炔衍生物的结构稳定性、原子构型和电子结构.本文计算的β石墨炔衍生物系列体系由六边形碳环(各边原子数N=1—10)通过顶点相连而成.对结构与能量的计算分析表明:当N为偶数时,β石墨炔拥有单、三键交替的C—C键结构,其能量比N为奇数时,拥有连续C=C双键的石墨炔衍生物更稳定.计算的能带结构和态密度显示:根据碳环各边原子个数N的奇偶性不同,β石墨炔可呈现金属性(N为奇数时)或半导体特性(N为偶数时).该奇偶依赖的原子构型和电学性质是由Jahn-Teller畸变效应导致,与碳环各边原子碳链的实际长度无关.计算发现部分半导体β石墨炔(N=2,6,10)呈现狄拉克锥能带特征,其带隙约10 meV,且具有0.255×10~6—0.414×10~6m/s的高电子速度,约为石墨烯电子速度的30%—50%.本密度泛函理论研究表明,将sp杂化碳原子引入石墨烯六边形碳环的边上,可通过控制六边形各边原子个数的奇偶性调制其金属和半导体电子特性或狄拉克锥的形成,为免掺杂和缺陷调控纳米碳材料的电学性质和设计碳基纳米电子器件提供了理论依据.     

单层Nb2SiTe4基化合物的带隙异常变化

传统硫族化合物中阳离子相同时,随着阴离子原子序数的增加,价带顶逐渐升高,带隙呈减小趋势.在A₂BX₄基(A=V,Nb,Ta;B=Si,Ge,Sn;X=S,Se,Te)化合物中,观察到随着阴离子原子序数增加,其带隙呈现反常增大的现象.为了探究其带隙异常变化的原因,基于第一性原理计算,对A₂BX₄基化合物的电子结构展开系统地研究,包括能带结构、带边相对位置、轨道间耦合作用以及能带宽度等影响.研究发现,Nb2SiX4基化合物中Nb原子4d轨道能量明显高于阴离子p轨道,其价带顶和导带底主要由Nb原子4d轨道相互作用组成,其带宽主要影响带隙大小.Nb₂SiX₄基化合物的带隙大小通过Nb—Nb和Nb—X键共同作用于Nb原子4d轨道的宽度来控制.当阴离子序数增加时,Nb—Nb键长增加,其相互作用减弱,由Nb原子4d轨道主导的能带变宽,带隙减小;另一方面,Nb—X键长增加又使Nb原子4d带宽变窄,带隙增加,并且Nb—X键长增长占主导,所以带隙最终呈现异常增加的趋势.     

PbTe(001)表面原子几何结构和电子结构的第一性原理计算

用第一性原理的密度泛函理论计算了PbTe（001）表面的几何结构和电子结构.计算结果表明：PbTe（001）表面不发生重构，但表面几层原子表现出明显的振荡弛豫现象，其中第一、第二层间距减小4.5%，第二、第三层间距增加2.0%，并且表面层原子出现褶皱.表面带隙在X 点，带隙变宽，在基本带隙中不引入新的表面态，而导带底和价带顶附近等多处出现新的表 面共振态；弛豫后费米面处态密度很低，所以表面结构很稳定. 关键词： 密度泛函理论 表面几何结构 表面电子结构 PbTe     

直接带隙Ge_(1-x)Sn_x本征载流子浓度研究

通过合金化改性技术,Ge可由间接带隙半导体转变为直接带隙半导体.改性后的Ge半导体可同时应用于光子器件和电子器件,极具发展潜力.基于直接带隙Ge1-x Sn x半导体合金8带Kronig-Penny模型,重点研究了其导带有效状态密度、价带有效状态密度及本征载流子浓度,旨在为直接带隙改性Ge半导体物理的理解及相关器件的研究设计提供有价值的参考.研究结果表明:直接带隙Ge1-x Sn x合金导带有效状态密度随着Sn组分x的增加而明显减小,价带有效状态密度几乎不随Sn组分变化.与体Ge半导体相比,直接带隙Ge1-x Sn x合金导带有效状态密度、价带有效状态密度分别低两个和一个数量级;直接带隙Ge1-x Sn x合金本征载流子浓度随着Sn组分的增加而增加,比体Ge半导体高一个数量级以上.     

N掺杂对α-石墨炔表面吸附H_2O,H,O和OH的电子性质和磁性的影响

石墨炔是一种新型的二维(2D)碳的同素异形体,炔键单元的高活性使其在小分子吸附方面相比石墨烯更具优势.本文基于密度泛函理论(DFT),研究了H_2O和H、O及OH分别在原始的和掺杂了N原子的α-石墨炔上的相互作用.研究结果表明,N掺杂和小分子吸附能够改变α-石墨炔的电子结构和磁性. N原子掺杂后α-石墨炔对小分子的吸附能力明显增强. H、O原子和OH吸附在N原子掺杂体系前后表现出明显的磁性差异:H原子和OH吸附在纯净的α-石墨炔上体系显示磁性,N原子掺杂后,磁性消失;而O原子则是吸附在纯净的α-石墨炔上未表现出磁性,N原子掺杂后,体系出现磁性.此外,α-石墨炔对水分子的吸附作用较弱,受范德瓦耳斯作用影响较大,属于物理吸附.本研究将为α-石墨炔中N杂质检测以及α-石墨炔基气体传感器的设计研究提供新的思路.     

石墨炔管能带和力学性质的第一性原理研究北大核心CSCD

基于第一性原理计算,研究了单壁锯齿型和扶手型石墨炔管的几何结构、电子结构以及杨氏模量．计算表明：石墨炔管是一类具有一定能隙的直接带隙半导体管,其带隙在0．4～1．3eV的能量范围,且随管径的增大而变小．而石墨炔管的杨氏模量在0．44～0．50Tpa区间变化．对于锯齿型石墨炔管,其杨氏模量随着半径的增大而变小而锯齿型石墨炔管的杨氏模量随其半径的增大而增大．     

Tailoring the photocatalytic activity of WO3 by Nb-F codoping from first-principles calculations

In this letter, the electronic structure properties of Nb, F monodoping and Nb-F codoping are explored by first-principles calculations. Our results show that Nb-F codoping can reduce the band gap notably. The band edge analysis indicates that both conduction band maximum (CBM) and valence band minimum (VBM) move to higher energies, which is desirable for water splitting. The formation energy and pair binding energy calculation shows that this anion-cation codoping is easy to realize in both O-rich and O-poor conditions. The calculated optical absorption spectra indicate that the visible light absorption can be significantly improved by Nb-F codoping in WO₃. Therefore, Nb-F co-doped WO₃ is predicted to be a promising visible light photocatalyst for water splitting.     

STUDY OF IRON OVERLAYER ON SULPHUR PASSIVATED GaAs(100) BY SYNCHROTRON RADIATION PHOTOEMISSION

We have studied the interface electronic structures and the chemical reaction of the Fe overlayer deposited on S-passivated GaAs(100). The chemical bond and electronic structure are different from Fe/GaAs, and the reaction between As and Fe is weakened by S atoms. This is beneficial to the magnetism in the interface. In the first stage of deposition, Fe clusters is form near S atoms due to the large electronegativity of S. The S atoms remain at the interface with Fe coverage. Magnetic ordering feature is found at a coverage higher than 0.6 nm. According to the large exchange splitting in valence band spectra, we suggest that Fe phase transition from bcc to fcc occurs with increasing coverage.     

直接带隙Ge$lt;sub$gt;1-$lt;em$gt;x$lt;/em$gt;$lt;/sub$gt;Sn$lt;sub$gt;$lt;em$gt;x$lt;/em$gt;$lt;/sub$gt;本征载流子浓度研究

通过合金化改性技术, Ge可由间接带隙半导体转变为直接带隙半导体. 改性后的Ge半导体可同时应用于光子器件和电子器件, 极具发展潜力. 基于直接带隙Ge_1-xSn_x半导体合金8带Kronig-Penny模型, 重点研究了其导带有效状态密度、价带有效状态密度及本征载流子浓度, 旨在为直接带隙改性Ge半导体物理的理解及相关器件的研究设计提供有价值的参考. 研究结果表明: 直接带隙Ge_1-xSn_x合金导带有效状态密度随着Sn组分x的增加而明显减小, 价带有效状态密度几乎不随Sn组分变化. 与体Ge半导体相比, 直接带隙Ge_1-xSn_x合金导带有效状态密度、价带有效状态密度分别低两个和一个数量级; 直接带隙Ge_1-xSn_x合金本征载流子浓度随着Sn组分的增加而增加, 比体Ge半导体高一个数量级以上. 关键词： 1-xSn_x')" href="#">Ge_1-xSn_x 直接带隙 本征载流子浓度     

Quantum chemical simulations of titanium dioxide nanotubes used for photocatalytic water splitting

Titanium dioxide nanotubes (NTs) built from various initial 2D models of TiO2 (a promising catalyst for water splitting) are investigated via density functional theory using the B3LYP hybrid exchange-correlation functional in the localized basis set of a linear combination of atomic orbitals. For TiO₂ NTs (eight different types of morphology) created from four initial 2D structures, full geometry optimization is performed and the main energy parameters, such as the band gap width, energy positions of the valence band top and the conduction band bottom, and NT formation and strain energy, are calculated. Analysis of the NT strain and formation energies enables us to choose their most stable configuration, which can further be employed to simulate NTs doped with impurity atoms capable of serving as efficient centers for the photocatalytic dissociation of water molecules.     

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.     

Benefits of oxygen in CuInSe2 and CuGaSe2 containing Se-rich grain boundaries

Using density functional theory calculation, we show that oxygen (O) exhibits an interesting effect in CuInSe₂ and CuGaSe₂. The Se atoms with dangling bonds in a Se-rich Σ3 (114) grain boundary (GB) create deep gap states due to strong interaction between Se atoms. However, when such a Se atom is substituted by an O atom, the deep gap states can be shifted into valence band, making the site no longer a harmful non-radiative recombination center. We find that O atoms prefer energetically to substitute these Se atoms and induce significant lattice relaxation due to their smaller atomic size and stronger electronegativity, which effectively reduces the anion–anion interaction. Consequently, the deep gap states are shifted to lower energy regions close or even below the top of the valence band.     

Influence of electronic structures of doped TiO2 on their photocatalysis

The modification of bandgap of TiO₂ was intensively studied for decades to improve its visible light absorbance efficiency. The practical application potential of TiO₂ as photocatalysts for water splitting and water purification has motivated enduring experimental and theoretical research of the doping effects in bulk and nanosized TiO₂ using transition metals, rear earths, p‐block metals and metalloids, and non‐metal elments as dopants to decrease the bandgap of TiO₂. This review summarized the typical theoretical results of the dopant induced variation in electronic structure, bandgap, and density of states of TiO₂. The codoping effects of metal/metal, metal/non‐metal combinations were also introduced briefly to display the modification of electronic structures. Some results were accompanied by experimental results to demonstrate the influence of improved light absorbance efficiency on the photocatalytic performance. The doping effects on the density of states of surface were also summarized briefly. The metal dopants show clear influences on the 3d electrons of titanium to elevate or depress the minimum of conduction band, while the non‐mental dopants mainly interact with the 2p electrons of oxygen to change the position of the maximum of the valence band. The review also noticed the theoretical development of the doping effect with the establishment of novel models, such as the water–TiO₂surface interaction. It should be noted that the theoretical models rarely consider the doping induced variation of defect types and concentration, Fermi level position, surface active sites, and charge transport due to the ground state simulation and shortcoming of density functional theory (DFT). The phenomenological explanations of the experimental results are arbitrary in most of the reports. A universal model is required to explain the complex dependence of the process of photocatalysis on the semiconducting properties, such as bandgap, Fermi level, charge transport, and surface states. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

H,F修饰单层GeTe的电子结构与光催化性质

采用基于密度泛函理论的第一性原理平面波赝势方法,计算了单层GeTe、表面氢化及氟化单层GeTe的晶体结构、稳定性、电子结构和光学性质.计算结果表明,经过修饰后, GeTe的晶格常数、键角、键长增大,且均具有较好的稳定性.电子结构分析表明,单层GeTe为间接带隙半导体,全氢化修饰、全氟化修饰以及氢氟共修饰(F, Ge同侧;H, Te同侧)则转变为直接带隙半导体,且修饰后的能隙均不同程度减小.载流子有效质量表明,全氢化、全氟化以及氢氟共修饰GeTe (F, Ge同侧;H, Te同侧)的有效质量减小,其载流子迁移率增强.带边势分析结果显示,单层GeTe能够光裂解水制氢和析氧,而修饰后的GeTe的价带带边势明显下移,其氧化性明显增强,能够光裂解水析O2, H2O2, O3以及OH·等产物.光学性质表明,修饰后的GeTe对可见光区和红、紫外区的光谱吸收效果明显增强,表明其在光催化领域有着广阔的应用前景.     

Possible effects of oxygen in Te-rich Σ3 (112) grain boundaries in CdTe

Using density functional theory calculation, we show that oxygen (O) exhibits an interesting effect in CdTe. The Te atoms with dangling bonds in a Te-rich rich Σ3 (112) grain boundary (GB) create deep gap states due to strong interaction between Te atoms. However, when such a Te atom is substituted by an O atom, the deep gap states can be shifted toward the valence band, making the site no longer a harmful non-radiative recombination center. We find that O atoms prefer energetically substituting these Te atoms and induce significant lattice relaxation due to their smaller atomic size and stronger electronegativity, which effectively reduces the anion–anion interaction. Consequently, the deep gap states are shifted to lower energy regions close to or even below the top of the valence band.     

Electronic structures of the F-terminated AlN nanoribbons

Using the first-principles calculations, electronic properties for the F-terminated AlN nanoribbons with both zigzag and armchair edges are studied. The results show that both the zigzag and armchair AlN nanoribbons are semiconducting and nonmagnetic, and the indirect band gap of the zigzag AlN nanoribbons and the direct band gap of the armchair ones decrease monotonically with increasing ribbon width. In contrast, the F-terminated AlN nanoribbons have narrower band gaps than those of the H-terminated ones when the ribbons have the same bandwidth. The density-of-states (DOS) and local density-of-states (LDOS) analyses show that the top of the valence band for the F-terminated ribbons is mainly contributed by N atoms, while at the side of the conduction band, the total DOS is mainly contributed by Al atoms. The charge density contour analyses show that Al–F bond is ionic because the electronegativity of F atom is much stronger for F atom than for Al atom, while N–F bond is covalent because of the combined action of the stronger electronegativity and the smaller covalent radius.