含能材料中键离解能的密度泛函理论计算

通过计算一个包括臭氧,硝基甲烷以及1,3,5 -三硝基-1,3,5-三氮杂环已烷(RDX)在内的典型系统的键离解能,对由四种交换/相关函数(BLYP,B3LYP,B3PW91和B3P86)加上不同的基函数组合而成的多种密度泛函方法的准确性进行了比较研究.结果表明:B3P86/6-31G**是计算该系统C-NO2,O-O和N-NO2键离解能的最可靠的方法.     

锑烯吸附金属Li原子的密度泛函研究

锑烯(antimonene)是继石墨烯和磷烯之后出现的新型二维材料,在锂离子电池等领域受到关注.本文基于第一性原理的密度泛函理论,计算研究了锑烯对Li原子的吸附特性,包括Li原子的最稳定吸附构型、吸附密度以及吸附Li原子的扩散路径.结果表明:Li原子最稳定的吸附位置位于谷位,即底层Sb原子之上、顶层三个Sb原子中心位置,吸附能为1.69 eV,吸附距离为2.81?;能带计算发现,锑烯为带隙宽度1.08 eV的间接带隙半导体,吸附Li原子后费米能级上升进入导带,呈现出金属性;原子分波态密度分析发现, Sb原子的p电子态和Li原子的p和s电子态形成明显的共振交叠,表现出杂化成键的特征;随着吸附Li原子数量增加,锑烯晶格结构和电子结构发生较大变化.通过微动弹性带方法计算发现, Li原子在锑烯表面的扩散势垒为0.07 eV,较小的势垒高度有利于快速充放电过程.     

分子束外延生长赝配高电子迁移率超高速微结构功能材料里深中心识别

应用深能级瞬态谱(DLTS)技术研究分子束外延(MBE)生长的highelectronmobilitytransistors(HEMT)和Pseudomorphichighelectronmobilitytransistors(PHEMT)结构深中心行为.样品的DLTS谱表明,在HEMT和PHEMT结构的nAlGaAs层里存在着较大浓度(1015-1017cm-3)和俘获截面(10-16cm2)的近禁带中部电子陷阱.它们可能与AlGaAs层的氧含量有关.同时还观察到PHEMT结构晶格不匹配的AlGaAsInGaAsGaAs系统在AlGaAs里产生的应力引起DX中心(与硅有关)能级位置的有序移动.其移动量可作为应力大小的一个判据,表明DLTS技术是定性识别此应力的可靠和简便的工具. 关键词： 分子束外延生长 高电子迁移率超高速微结构功能材料 深中心     

Proposal of the readout electronics for the WCDA in the LHAASO experiment

The LHAASO （Large High Altitude Air Shower Observatory） experiment is proposed for a very high energy gamma ray source survey, in which the WCDA （Water Cherellkov Detector Array） is one of the major coinponents. In the WCDA, a total of 3600 PMTs are placed under water in four ponds, each with a size of 150m×150 m. Precise time and cimrge measurement is required for the PMT signals, over a large signal amplitude range from a single P.E. （photo electron） to 4000 P.E. To fulfill the high requirement of a signal measurement in so many front end nodes scattered in a large area, special techniques are developed, such as multiple gain readout, hybrid transmission of clocks, commands and data, precise clock phase alignment and new trigger electronics. We present the readout electronics architecture for the WCDA and several prototype modules, which are now being testedin the laboratory.     

Proposal of the readout electronics for the WCDA in the LHAASO experiment

The LHAASO(Large High Altitude Air Shower Observatory)experiment is proposed for a very high energy gamma ray source survey,in which the WCDA(Water Cherenkov Detector Array)is one of the major components.In the WCDA,a total of 3600 PMTs are placed under water in four ponds,each with a size of150 m×l50 m.Precise time and charge measurement is required for the PMT signals,over a large signal amplitude range from a single P.E.(photo electron)to 4000 P.E.To fulfill the high requirement of a signal measurement in so many front end nodes scattered in a large area,special techniques are developed,such as multiple gain readout,hybrid transmission of clocks,commands and data,precise clock phase alignment and new trigger electronics.We present the readout electronics architecture for the WCDA and several prototype modules,which are now being tested in the laboratory.     

Advances and challenges in DFT-based energy materials design

The growing worldwide energy needs call for developing novel materials for energy applications. Ab initio density functional theory (DFT) calculations allow the understanding and prediction of material properties at the atomic scale, thus, play an important role in energy materials design. Due to the fast progress of computer power and development of calculation methodologies, DFT-based calculations have greatly improved their predictive power, and are now leading to a paradigm shift towards theory-driven materials design. The aim of this perspective is to introduce the advances in DFT calculations which accelerate energy materials design. We first present state-of-the-art DFT methods for accurate simulation of various key properties of energy materials. Then we show examples of how these advances lead to the discovery of new energy materials for photovoltaic, photocatalytic, thermoelectric, and battery applications. The challenges and future research directions in computational design of energy materials are highlighted at the end.     

Two-dimensional MTe2 (M = Co,Fe, Mn,Sc, Ti) transition metal tellurides as sodium ion battery anode materials: Density functional theory calculations

We performed density functional theory calculations to probe sodium adsorption and diffusion properties on two-dimensional (2D) MTe₂ (M = Co, Fe, Mn, Sc, Ti) first-row transition metal tellurides, and gauge their potentials as anode materials for sodium-ion batteries (NIBs). In this work, we found that all considered MTe₂ possess strong sodium adsorption properties and excellent diffusion kinetics. Moreover, sodium atoms prefer to bind on sites that are farther apart rather than on nearby sites, implying that (1) the sodium clustering is not favored and (2) the large adsorption energies are essentially due to the sodium-MTe₂ interaction. We further adopted ab initio random structure search to compute probable stable sodium adsorption configurations, to obtain more accurate capacities and open circuit voltages. The calculated capacities and open circuit voltage are reasonable, and are suitable for anode applications. Our results show that in general, 2D MTe₂ sheets have suitable sodium adsorption energies and diffusion barriers, and could be applied as sodium ion battery anode materials.     

The rise of two-dimensional tellurium for next-generation electronics and optoelectronics

Single-element two-dimensional (2D) tellurium (Te) which possesses an unusual quasi-one-dimensional atomic chain structure is a new member in 2D materials family. 2D Te possesses high carrier mobility, wide tunable bandgap, strong light-matter interaction, better environmental stability, and strong anisotropy, making Te exhibit tremendous application potential in next-generation electronic and optoelectronic devices. However, as an emerging 2D material, the research on fundamental property and device application of Te is still in its infancy. Hence, this review summarizes the most recent research progresses about the new star 2D Te and discusses its future development direction. Firstly, the structural features, basic physical properties, and various preparation methods of 2D Te are systemically introduced. Then, we emphatically summarize the booming development of 2D Te-based electronic and optoelectronic devices including field effect transistors, photodetectors and van der Waals heterostructure photodiodes. Finally, the future challenges, opportunities, and development directions of 2D Te-based electronic and optoelectronic devices are prospected.     

Effect of metal atoms on the electronic properties of metal oxide nanoclusters for use in drug delivery applications: a density functional theory study

To improve drug selectivity toward target cells, one interesting technique for drug delivery is to use nanostructured materials. Recent studies revealed that the fullerene-like nanoclusters can pass through cell walls and transport and release drugs in the target site. In this study, the reactivity, and electronic sensitivity of the Be12O12, Mg12O12, and Zn12O12 nanoclusters were investigated toward hydroxyurea (HU) anticancer drug using density functional theory calculations at gas phase and aqueous solution. Our results show that the electronic properties of Mg12O12 and Zn12O12 nanoclusters are significantly sensitive to the presence of HU and the nanoclusters may be a promising candidate for adsorption of this drug. The results show that all complexes are energetically favourable, especially in the aqueous phase. Also, our ultraviolet–visible results show that the electronic spectra of HU/(MO)12 complexes exhibit a blue shift toward lower wavelengths (higher energies). To go further and gain insight into the binding features of considered (MO)12 nanoclusters with HU drug, the Atoms in Molecules analysis was performed. Our results determine the electrostatic features of the HU/Mg12O12 and HU/Zn12O12 bonding. Consequently, the results demonstrated that the Mg12O12 and Zn12O12 nanoclusters could be used as potential carriers for the delivery of HU drug.     

利用Taylor展开法研究Lamb波在功能梯度材料中的传播特性

超声技术可用于对功能梯度材料(FGMs)的性质进行评估. 由于FGMs性质的非均匀性,采用分布函数来描述FGMs弹性常数和密度沿厚度方向的变化趋势,并提出利用Taylor展开的方法来解决分布函数为任意函数时的FGMs中Lamb波的传播问题. 利用本征函数展开法得到了铁基氧化铝FGMs中Lamb波的相速度色散曲线,讨论了材料性质分布对铁基氧化铝FGMs中Lamb波传播特性的影响. 为FGMs性质(沿板厚方向变化)的反演提供了理论依据. 关键词： 功能梯度材料 Lamb波 Legendre多项式 分布函数     

BaO/W(1 0 0) thermionic emitters and the effects of Sc, Y, La, and the density functional used in computations

Density functional theory is used to predict workfunctions, φ. For relaxed clean W(1 0 0), the local density approximation (LDA) agrees with experiment better than the newer generalized gradient approximation, probably due to the surface electron self-energy. The large Ba metallic radius indicates it covers W(1 0 0) at about 0.5 monolayer (ML). However, Ba²⁺, O²⁻, and metallic W all have similar radii. Thus 1 ML of BaO (one BaO unit for each two W atoms) produces minimum strain, indicating commensurate interfaces. BaO (1 ML) and Ba (1/2 ML) have the sameφ to within 0.02 V, so at these coverages reduction or oxidation is not important. Due to greater chemical activity of ScO vs. highly ionic BaO, when mixing the latter with this suboxide of scandia, the overlayer always has BaO as the top layer and ScO as the second layer. The BaO/ScO bilayer has a rocksalt structure, suggesting high stability. In the series BaO/ScO/, BaO/YO/, and BaO/LaO/W(1 0 0), the latter has a remarkably low φ of 1.3 V (LDA), but 2 ML of rocksalt BaO also has φ at 1.3 V. We suggest BaO (1 ML) does not exist and that it is worthwhile to attempt the direct synthesis and study of BaO (2 ML) and BaO/LaO.     

Modeling of heterogeneous surfaces and characterization of porous materials by extending density functional theory for the case of amorphous solids

A method of characterization of carbonaceous materials using nongraphitized carbon black as a reference is considered. The Tarazona density functional theory was applied to amorphous solids to describe nitrogen adsorption on nongraphitized carbon black. This allows us to describe energetic heterogeneity without the need to invoke any energy distribution functions. To derive the pore size distribution (PSD) of porous carbon whose pore walls are non-graphitized, we used the entropy concept in the regularization method. With this approach PSD is more well-behaved than that obtained with the usual means. We applied this new theory to study the effects of technological parameters on porous structure of a series of activated carbon.     

全密度功能性复杂金属零件的激光直接快速制造

 针对具有复杂结构的全密度功能性金属零件快速制造难题,探讨了该类零件的选区激光熔化直接快速制造方法,并结合实验,重点对同步保证选区激光熔化快速制造金属零件成型密度及精度的工艺进行了研究。结果表明：同步消除球化、飞溅及气孔对成型件致密性及精度的影响是实现选区激光熔化快速制造全密度功能性复杂金属零件的难点及关键;在维持良好的抗氧化气氛条件下,可采用尽可能薄的铺粉厚度及恰当调节其它成型参数的方法,以保证对上一层有足够的重熔量来消除球化及气孔现象;同时,采用合适的扫描策略,可弱化飞溅对成型质量的影响来解决工艺难题。采用该工艺方案可快速制造全密度功能性复杂金属零件,所成型的316L不锈钢叶轮零件相对密度为99.8%,硬度为HB192,表面粗糙度约为40 μm,尺寸精度在±0.1 mm以内,稍经打磨后即可投入使用。     

新型空穴传输材料在钙钛矿太阳能电池中的研究进展

钙钛矿太阳能电池是一种全新的全固态薄膜电池. 报道的能量转换效率已提高到19.3%, 成为可再生能源领域的热点研究方向. 空穴传输材料是构成高效钙钛矿太阳能电池的重要组分之一. 本文介绍了钙钛矿太阳能电池的基本结构, 对空穴传输材料的分子结构、能级水平和迁移率等对电池性能的影响进行了详细的总结和评述.     

Adsorption of argon and nitrogen in cylindrical pores of MCM-41 materials: application of density functional theory

Adsorption of argon and nitrogen at their respective boiling points in cylindrical pores of MCM-41 type silica-like adsorbents is studied by means of a non-local density functional theory (NLDFT), which is modified to deal with amorphous solids. By matching the theoretical results of the pore filling pressure versus pore diameter against the experimental data, we arrive at a conclusion that the adsorption branch (rather than desorption) corresponds to the true thermodynamic equilibrium. If this is accepted, we derive the optimal values for the solid-fluid molecular parameters for the system amorphous silica-Ar and amorphous silica-N₂, and at the same time we could derive reliably the specific surface area of non-porous and mesoporous silica-like adsorbents, without a recourse to the BET method. This method is then logically extended to describe the local adsorption isotherms of argon and nitrogen in silica-like pores, which are then used as the bases (kernel) to determine the pore size distribution. We test this with a number of adsorption isotherms on the MCM-41 samples, and the results are quite realistic and in excellent agreement with the XRD results, justifying the approach adopted in this paper.     

Computational screening of doping schemes for LiTi_2(PO_4)_3 as cathode coating materials

In all-solid-state lithium batteries,the impedance at the cathode/electrolyte interface shows close relationship with the cycle performance.Cathode coatings are helpful to reduce the impedance and increase the stability at the interface effectively.LiTi2(PO4)3(LTP),a fast ion conductor with high ionic conductivity approaching 10^-3S·cm^-1,is adopted as the coating materials in this study.The crystal and electronic structures,as well as the Li^+ion migration properties are evaluated for LTP and its doped derivatives based on density functional theory(DFT)and bond valence(BV)method.Substituting part of Ti sites with element Mn,Fe,or Mg in LTP can improve the electronic conductivity of LTP while does not decrease its high ionic conductivity.In this way,the coating materials with both high ionic conductivities and electronic conductivities can be prepared for all-solid-state lithium batteries to improve the ion and electron transport properties at the interface.     

全密度功能性复杂金属零件的激光直接快速制造

针对具有复杂结构的全密度功能性金属零件快速制造难题,探讨了该类零件的选区激光熔化直接快速制造方法,并结合实验,重点对同步保证选区激光熔化快速制造金属零件成型密度及精度的工艺进行了研究。结果表明：同步消除球化、飞溅及气孔对成型件致密性及精度的影响是实现选区激光熔化快速制造全密度功能性复杂金属零件的难点及关键;在维持良好的抗氧化气氛条件下,可采用尽可能薄的铺粉厚度及恰当调节其它成型参数的方法,以保证对上一层有足够的重熔量来消除球化及气孔现象;同时,采用合适的扫描策略,可弱化飞溅对成型质量的影响来解决工艺难题。采用该工艺方案可快速制造全密度功能性复杂金属零件,所成型的316L不锈钢叶轮零件相对密度为99.8%,硬度为HB192,表面粗糙度约为40 μm,尺寸精度在±0.1 mm以内,稍经打磨后即可投入使用。     

A dislocation-based stress-strain gradient plasticity model for strength and ductility in materials with gradient microstructures

Although metallic materials with gradient microstructure exhibit notable performance in harsh environmental conditions, they can also exhibit unusual mechanical behaviour. This is attributed to both grain size and the gradient of grain size distribution in the structure. Metallic materials with a homogenous distribution of grain size follow the traditional Hall-Petch relationship, in which strength increases with decreasing grain size at the expense of ductility. However, studies show that materials with a gradient of grain size microstructure do not follow the Hall-Petch relationship, and thus have improved strength and ductility. This suggests that with creative design and engineering of microstructure, the strength-ductility trade-off can be reduced or prevented.

In this study, we developed and implemented a dislocation density based model to investigate the mechanical behaviour of nano-microstructure. We designed a multi-scale modelling framework, coupling VPSC (Viscoplastic Self Consistent model) with CDD (Continuum Dislocation Dynamics), applying crystal plasticity equations to simulate dislocation interaction in polycrystalline metallic materials. We also developed design parameters and a model to predict the strength and ductility of materials with gradient microstructure.     

Surface segregation energies in low-index open surfaces of bimetallic transition metal alloys

We present a database of 24 × 24 segregation energies of single transition metal impurities in low-index surfaces of transition metal hosts, calculated using the localized self-consistent Green’s function (LSGF) method, in combination with the atomic sphere approximation including a multipole correction to the electrostatic potential and energy. The surface energies of facets for fcc and bcc transition metals, and the more stable of the two facets of hcp transition metals are also calculated and compared with available theoretical results. Insights derived should be useful for determining the nature of active sites in a variety of catalytic reactions employing bimetallic catalysts.     

Effects of the metal in the adsorption of NO2 on platinum supported BaO films

Density functional calculations are reported for NO₂ adsorption on BaO(1 0 0) films supported on Pt. The metal is predicted to largely stabilize NO₂ adsorption. The phenomenon is most pronounced for a two layer BaO film, but clearly present for films as thick as five oxide layers. From the different contributions to the adsorption energy, the stabilization is found to originate from an increased oxide-metal bonding. The results stress the complex nature of molecular-surface interactions in multi-component systems, and have implications for the understanding of surface processes in heterogeneous catalysis.