Titanium Trisulfide Monolayer: Theoretical Prediction of a New Direct‐Gap Semiconductor with High and Anisotropic Carrier Mobility

A new two‐dimensional (2D) layered material, namely, titanium trisulfide (TiS₃) monolayer, is predicted to possess novel electronic properties. Ab initio calculations show that the perfect TiS₃ monolayer is a direct‐gap semiconductor with a bandgap of 1.02 eV, close to that of bulk silicon, and with high carrier mobility. More remarkably, the in‐plane electron mobility of the 2D TiS₃ is highly anisotropic, amounting to about 10 000 cm² V^?1 s^?1 in the b direction, which is higher than that of the MoS₂ monolayer, whereas the hole mobility is about two orders of magnitude lower. Furthermore, TiS₃ possesses lower cleavage energy than graphite, suggesting easy exfoliation for TiS₃. Both dynamical and thermal stability of the TiS₃ monolayer is examined by phonon‐spectrum calculation and Born–Oppenheimer molecular dynamics simulation. The desired electronic properties render the TiS₃ monolayer a promising 2D atomic‐layer material for applications in future nanoelectronics.     

Functional Corannulene: Diverse Structures,Enhanced Charge Transport,and Tunable Optoelectronic Properties

Chemical functionalization of various hydrocarbons, such as coronene, corannulene, and so forth, shows good promise in electronics applications because of their tunable optoelectronic properties. By using quantum chemical calculations, we have investigated the changes in the corannulene buckybowl structure, which greatly affect its electronic and optical properties when functionalized with different electron‐withdrawing imide groups. We find that the chemical nature and position of functional groups strongly regulate the stacking geometry, π‐stacking interactions, and electronic structure. Herein, a range of optoelectronic properties and structure–property relationships of various imide‐functionalized corannulenes are explored and rationalized in detail. In terms of carrier mobility, we find that the functionalization strongly affects the reorganization energy of corannulene, while the enhanced stacking improves hopping integrals, favoring the carrier mobility of crystals of pentafluorophenylcorannulene‐5‐monoimide. The study shows a host of emerging optoelectronic properties and enhancements in the charge‐transport characteristics of functionalized corannulene, which may find possible semiconductor and electronics applications.     

Optoelectronic and charge transport properties of the complex of carbon nanotube with perylene bisimide

In the present study we carried out an investigation on the structure and properties of the complex formed by adsorbing perylene bisimide (PBI) on the surface of (6,6) carbon nanotube (CNT) by employing different dispersion-corrected density functionals (B97D, B3LYP-GD3, and ωB97XD), which showed the complex as stable. The contribution of various components of interaction energy follows the order: dispersion > electrostatic > induction. The lower ionization energy of CNT and the higher electron affinity of PBI revealed that they constitute a donor-acceptor system. Electron density distribution of the frontier molecular orbitals of complex confirmed the photoinduced charge transfer. The charge transport properties of the complex indicated higher hole mobility than electron mobility making it suitable to be used as p-type transistor. The absorption spectrum of the complex showed absorption in the near ultraviolet-visible-near infrared regions of the electromagnetic spectrum suggesting it useful for solar cells.     

Two‐Dimensional Haeckelite NbS2: A Diamagnetic High‐Mobility Semiconductor with Nb4+ Ions

In all known Group 5 transition‐metal dichalcogenide monolayers (MLs), the metal centers carry a spin, and their ground‐state phases are either metallic or semiconducting with indirect band gaps. Here, on grounds of first‐principles calculations, we report that the Haeckelite polytypes 1 S ‐NbX₂ (X=S, Se, Te) are diamagnetic direct‐band‐gap semiconductors even though the Nb atoms are in the 4+ oxidation state. In contrast, 1 S ‐VX₂ MLs are antiferromagnetically coupled indirect‐band‐gap semiconductors. The 1 S phases are thermodynamically and dynamically stable but of slightly higher energy than their 1 H and 1 T ML counterparts. 1 S ‐NbX₂ MLs are excellent candidates for optoelectronic applications owing to their small band gaps (between 0.5 and 1 eV). Moreover, 1 S ‐NbS₂ shows a particularly high hole mobility of 2.68×10³ cm² V⁻¹ s⁻¹, which is significantly higher than that of MoS₂ and comparable to that of WSe₂.     

Electronic Properties of Armchair Graphene Nanoribbons with Oxygen-terminated Edges: A Density Functional Study

Armchair graphene nanoribbons with different proportions of edge oxygen atoms are analyzed in this study using the crystal orbital method,which is based on density functional theory.Although buckled edges are present,all the nanoribbons are energetically favorable.Unlike the adjacent edge oxygen atoms,the isolated edge oxygen atoms cause semiconductor-metal transitions by introducing edge states.For graphene nanoribbons with all oxygen atoms on the edges,band gap and carrier mobility vary with ribbon width.Furthermore,this behavior is different from that of hydrogen-passivated graphene nanoribbons because of different effective widths,which are pictorially presented with crystal orbitals.The carrier mobilities are as 18%~65% magnitude as those of hydrogen-passivated nanoribbons and are of the order of 103 cm2·V-1·s-1.     

SinH/SinH-(n=3～8)的结构和电子亲合能的研究

选用四种不同的密度泛函理论方法(B3LYP，B3P86，BLYP，BP86)，在全电子的双ξ加极化加弥散函数基组(DZP )下，对SinH／SinH^-(n=3～8)体系进行研究，获得它们的基态结构和电子亲合能。预测Si3H／Si3H^-,Si4H／Si4H^-,Si5H／Si5H^-,Si6H／Si6H^-，Si7H／Si7H^-和Si8H／Si8H^-的基态结构分别为C2v(^2B2)／C2v(1^A1)氢桥结构，Cs(^2A’)／C(^1A’)，C2v(^2B2)／C2v(^1A1)，C2v(^2B2或^2B1)／C4v(^1A1)，C5v(^2A1)／C5v(^1A1)和C5(^2A‘‘)／C3v(^1A1)。在电子亲合能方面，B3LYP方法预测的电子亲合能是最可靠的，预测Si3H，Si4H，Si5H，Si6H，Si7H和Si8H的电子亲合能分别为2．56，2．59，2．84，2．86，3．19和3．14eV。     

Recent Advances in Surface Modifications of Elemental Two-Dimensional Materials: Structures,Properties, and Applications

The advent of graphene opens up the research into two-dimensional (2D) materials, which are considered revolutionary materials. Due to its unique geometric structure, graphene exhibits a series of exotic physical and chemical properties. In addition, single-element-based 2D materials (Xenes) have garnered tremendous interest. At present, 16 kinds of Xenes (silicene, borophene, germanene, phosphorene, tellurene, etc.) have been explored, mainly distributed in the third, fourth, fifth, and sixth main groups. The current methods to prepare monolayers or few-layer 2D materials include epitaxy growth, mechanical exfoliation, and liquid phase exfoliation. Although two Xenes (aluminene and indiene) have not been synthesized due to the limitations of synthetic methods and the stability of Xenes, other Xenes have been successfully created via elaborate artificial design and synthesis. Focusing on elemental 2D materials, this review mainly summarizes the recently reported work about tuning the electronic, optical, mechanical, and chemical properties of Xenes via surface modifications, achieved using controllable approaches (doping, adsorption, strain, intercalation, phase transition, etc.) to broaden their applications in various fields, including spintronics, electronics, optoelectronics, superconducting, photovoltaics, sensors, catalysis, and biomedicines. These advances in the surface modification of Xenes have laid a theoretical and experimental foundation for the development of 2D materials and their practical applications in diverse fields.     

Intrinsically Low Thermal Conductivity and High Carrier Mobility in Dual Topological Quantum Material,n‐Type BiTe

A challenge in thermoelectrics is to achieve intrinsically low thermal conductivity in crystalline solids while maintaining a high carrier mobility (μ). Topological quantum materials, such as the topological insulator (TI) or topological crystalline insulator (TCI) can exhibit high μ. Weak topological insulators (WTI) are of interest because of their layered hetero‐structural nature which has a low lattice thermal conductivity (κ_lat). BiTe, a unique member of the (Bi₂)_m(Bi₂Te₃)_n homologous series (m:n=1:2), has both the quantum states, TCI and WTI, which is distinct from the conventional strong TI, Bi₂Te₃ (where m:n=0:1). Herein, we report intrinsically low κ_lat of 0.47–0.8 W m^?1 K^?1 in the 300–650 K range in BiTe resulting from low energy optical phonon branches which originate primarily from the localized vibrations of Bi bilayer. It has high μ≈516 cm² V^?1 s^?1 and 707 cm² V^?1 s^?1 along parallel and perpendicular to the spark plasma sintering (SPS) directions, respectively, at room temperature.     

[Hg6O8]4- Group in Mercury Oxohalides: Real Structures and Quantum-Chemical Calculation

For oxohalides of bivalent mercury [electronic configuration Hg(5d¹⁰)] containing [Hg₄O₅]^2- tetrahedral and [Hg₆O₈]^4- octahedral mercury groups, crystal-chemical and quantum-chemical analyses have been carried out. Density functional theory calculations indicate that the stability of these cluster groups of Hg²⁺ ions primarily depends on the contribution of scalar relativistic corrections and spin-orbital coupling.     

用含时密度泛函方法研究和设计推拉结构的荧光分子

应用密度泛函理论(DFT)和含时密度泛函理论(TDDFT)方法及连续极化模型研究了六种荧光材料分子基态和第一激发态的电子结构性质.这六种分子是:3-(二氰亚甲基)-5,5-二甲基-1-(3-[9-(2-乙基-己基)-咔唑基]-乙烯基)环己烷(DCDHCC),DCDHCC2,3-(二氰亚甲基)-5,5-二甲基-1-(4-二苯基氨基-苯乙烯基)环己烷(DCDPC),DCDPC2,3-(二氰亚甲基)-5,5-二甲基-1-(4-[9-咔唑基]-乙烯基)环己烷(DCDCC)和3-(二氰亚甲基)-5,5-二甲基-1-(4-二甲基氨基-苯乙烯基)环己烷(DCDDC).它们可作为有机发光显示器件的发光材料.比较了PBE0、M06、BMK、M062X和CAM-B3LYP五种泛函,其中BMK方法很好地再现了各个分子在丙酮溶剂中的吸收和发射光谱.同时计算了分子的电子亲和能和电离势并用于评价分子的电荷注入性质.研究表明,当使用双π桥和双受体时,分子的发射光谱会红移到理想的发光区域.据此设计了两个新的分子DCDCC2和DCDDC2,它们分别是DCDCC和DCDDC的双支对应分子.计算结果表明这两个分子也具有作为荧光发射体的良好性质.     

CO2在Fe3O4(111)表面的吸附结构及能量研究

利用密度泛函理论研究了CO₂在Fe₃O₄（111）表面Fe_tet1和Fe_oct2两种终结的吸附行为。在Fe_tet1终结表面,当覆盖度为1/5 ML时,CO₂倾向于线性吸附;而在高覆盖度下,弯曲的CO₂与表面O作用形成CO₃^2-结构。在Fe_oct2终结表面,CO₂倾向于弯曲吸附,在1/6 ML和1/3 ML覆盖度时都可以形成CO₃^2-和-COO结构。覆盖度对Fe_tet1终结的表面影响很弱,但是对Fe_oct2终结的表面影响很大。从热力学上来说,CO₂在Fe_oct2终结表面的吸附要比Fe_tet1终结表面更有利。     

端基对二噻吩和苯并噻吩类共轭桥化合物电子结构及载流子传输性能的影响

采用密度泛函理论(DFT, TDDFT) B3LYP/6-31G(d)和PBE0/6-31G(d)方法对苯乙烯/乙炔为端基, 二噻吩(2T)、苯并二噻吩(TPT)和二苯并噻吩(PTP)为共轭桥的12个化合物进行了系统地计算研究. 在分别优化中性态与离子态几何构型的基础上, 获得了前线轨道能级、电离能(IPs)、电子亲合能(EAs)、重组能(λ_h/λ_e)和电子吸收光谱等信息. 结果表明, 苯乙炔基取代苯乙烯基对LUMO能级影响很小, 但HOMO能级明显降低, 能级差?E和激发能E_v增大, 吸收光谱蓝移10～30 nm, 多数苯乙炔基化合物的重组能均有所降低|端基相同共轭桥分别为2T, TPT和PTP时, HOMO能级逐渐降低, LUMO能级逐渐升高, ?E和E_v依次增大, 吸收光谱依次蓝移30～45 nm. 研究结果还表明, TPT共轭桥化合物的重组能较小, 且λ_h与λ_e相近, 有利于载流子传输平衡, 提高传输速率. 本文设计的苯乙炔基苯并二噻吩(DPATPT)有望成为潜在的传输效率高、抗氧化能力强的载流子传输材料.     

1，2，5-噻重氮和1，4-二正戊氧基苯环化的自由四氮杂卟啉及其金属镁配合物的结构和性质：密度泛函理论计算

用DFT方法计算分析了1，2，5-噻重氮和1，4-二正戊氧基苯环化的自由四氮杂卟啉及其金属镁配合物的分子和电子结构，理论计算的键参数和单晶结构测定结果一致。进一步对1，2，5-噻重氮和1，4-二正戊氧基苯环化的自由四氮杂卟啉的红外光谱进行了正则坐标分析和光谱模拟，以及用TD-DFT方法对1，2，5-噻重氮和1，4-二正戊氧基苯环化的四氮杂卟啉金属镁配合物的电子吸收光谱进行了分析和谱峰归属，比较了四氮杂卟啉环上取代基的电子性质对四氮杂卟啉衍生物光谱性质的影响。     

Theoretical Studies on the Molecular Structures and Thermodynamic Properties of Polychlorinated Fluorenes

Geometric structures of 135 polychlorinated fluorene (PCFR) molecules were optimized using density functional theory (DFT) at the B3LYP/6-311G** level and their thermodynamic properties in the ideal gas state were calculated. The relations of these thermodynamic properties with the number and position of chlorine atoms were also explored, from which the relative stability of PCFR congeners was theoretically proposed according to the magnitude of the relative standard Gibbs free energy of formation (Δr,fGθ). The results show that the geometric configuration of PCFR isomers is determined by the position of chlorine atoms. There exist two types of intramolecular weak interactions, i.e., C-H···Cl and Cl···Cl interactions in PCFR molecules. The change of ΔfHθ and ΔfGθ of most stable PCFR isomers with increasing the number of chlorine atoms is different from that in most unstable PCFR congeners. The values of ΔfHθ and ΔfGθ for PCFR isomers with the same number of chlorine atoms strongly depend on the position of chlorine atoms and the relative stability of PCFR congeners is mainly determined by intramolecular delocalized π bond and Cl···Cl nuclear repulsive interaction.     

非绝热分子动力学模拟A位阳离子对钙钛矿热载流子弛豫的影响

钙钛矿具有优异的光学和电学性质,近年来成为太阳能电池领域的研究热点.大量实验报道钙钛矿热载流子弛豫时间变化顺序为CsPbBr₃>MAPbBr₃(MA=CH₃NH₃)>FAPbBr₃[FA=HC(NH₂)₂],但A位阳离子(Cs⁺,MA⁺,FA⁺)对弛豫快慢的影响机制仍不明确.采用基于含时密度泛函理论的非绝热动力学方法研究了上述3种钙钛矿热电子和热空穴的能量弛豫动力学,计算得到的热载流子弛豫时间与实验结果吻合.结果表明,A位阳离子通过静电和氢键作用影响其与无机Pb—Br骨架的电子-振动耦合,使非绝热耦合强度遵从FAPbBr₃>MAPbBr₃>CsPbBr₃的变化趋势,进而使热载流子弛豫时间尺度变化趋势与之相同,表明合理选择A位阳离子可以优化钙钛矿太阳能电池的性能.     

Theoretical Studies on the Molecular Structures and Thermodynamic Properties of Polychlorinated Acenaphthylenes

Geometric structures of 135 polychlorinated acenaphthylene (PCAC) molecules were optimized using density functional theory (DFT) at the B3LYP/6-311G** level and some thermodynamic properties of them in the ideal gas state were calculated. The relations of these thermodynamic properties with the number and position of chlorine atoms were also explored, from which the relative stability of PCAC congeners was theoretically proposed according to the magnitude of the relative standard Gibbs free energy of formation (△r,fGθ). The results show that all PCAC isomers have planar geometric configuration. There exists intramolecular Cl···Cl weak interaction in some PCAC molecules. The change of △fHθ and fGθ of most stable PCAC isomers with increasing the number of chlorine atoms is different from that in the least stable PCAC congeners. The values of fHθ and fGθ for PCAC isomers with the same number of chlorine atoms show a strong dependence on the position of chlorine atoms and the relative stability of PCAC congeners has close relation with the intramolecular Cl···Cl nuclear repulsive interaction.     

Electronic Structures and Thermoelectric Properties of Two-Dimensional MoS2/MoSe2 Heterostructures

Thermoelectric properties of bulk and bilayer two-dimensional (2D) MoS₂/MoSe₂ heterostructures are investigated using density functional theory in conjunction with semiclassical Boltzmann transport theory. It is predicted that the bulk 2D heterostructures could considerably enhance the thermoelectric properties as compared with the bulk MoSe₂. The enhancement originates from the reduction in the band gap and the presence of interlayer van der Waals interactions. We therefore propose the 2D MoS₂/MoSe₂ heterostructures as a possible candidate material for thermoelectric applications.     

Endohedral Metallofullerenes: New Structures and Unseen Phenomena

Endohedral metallofullerenes (EMFs), namely fullerenes with metallic species encapsulated inside, represent an ideal platform to investigate metal–metal or metal–carbon interactions at the sub-nanometer scale by means of single-crystal X-ray diffraction (XRD) crystallography. Herein, recent progress in the identification of new structures and unprecedented properties are discussed according to the categories of monometallofullerenes, dimetallofullerenes, carbide clusterfullerenes, and nitride clusterfullerenes. In particular, the dimerization and the cage-isomer dependent oxidation state of the inner metal atom are summarized in terms of pristine monometallofullerenes. Metal–metal bonds involving lanthanide–lanthanides or actinide–actinides are discussed based on both experimental and theoretical studies. The cluster–cage matching and/or mutual selections, as well as the rarely seen M=C double bonds, are discovered in M₂C₂@C_2n, U₂C@C₈₀, M₂TiC@C₈₀, and Ti₃C₃@C₈₀. Subsequently, the geometries of different M₃N clusters in various cages are discussed, revealing size-matching between the internal M₃N cluster and the outer cage induced by the planarity of the cluster. Finally, an outlook regarding the future developments of the molecular structures and applications of EMFs is presented.     

Two-Dimensional VDW Crystal SnP3 with High Carrier Mobility and Extraordinary Sunlight Absorbance

Although bulk SnP₃ has been fabricated by experiments in the 1970’s, its electronic and optical properties within several layers have not been reported. Here, based on first-principles calculations, we have predicted two-dimensional SnP₃ layers as new semiconducting materials that possess indirect band gaps of 0.71 eV (monolayer) and 1.03 eV (bilayer), which are different from the metallic character of bulk structure. Remarkably, 2D SnP₃ possesses high hole mobility of 9.171×10⁴ cm²?V^-1?s^-1 and high light absorption (∽10⁶ cm^-1) in the whole visible spectrum, which predicts 2D SnP₃ layers as prospective candidates for nanoelectronics and photovoltaics. Interestingly, we found that 2D SnP₃ bilayer shows similar electronic and optical characters of silicon.     

双环-HMX结构和性质的理论研究

在DFT-B3LYP/6-311G*水平上, 计算研究了高能化合物四硝基四氮杂双环辛烷(双环-HMX) α和β两种异构体的结构和性质. 比较分子对称性、分子内氢键和环张力等几何参数以及分子总能量和前线轨道能级等电子结构参数, 发现α比β稳定. 分子中N—N键较长, N—N键集居数较小, 预示该键为热解和起爆的引发键. 基于简谐振动分析求得IR谱频率和强度. 运用统计热力学方法求得200～1000 K温度的热力学性质. 以非限制性半经验PM3方法探讨其热解机理, 求得各反应通道的过渡态和活化能, 发现热解始于侧链N—NO₂键的均裂. 还从理论上预测了该化合物的密度、爆速和爆压, 有助于寻求高能量密度材料(HEDM).