GO/Ti基复合材料界面性质的第一性原理研究

目的 研究氧化石墨烯在继承石墨烯优异性能的同时,是否会因为官能团的存在而影响复合材料界面的结合方式,抑制脆性相TiC的产生,解决石墨烯作为增强体时易发生界面反应从而影响材料塑韧性的问题。方法 根据(0001)Ti∥(0001)GO、 ∥ 界面位向关系,建立了Ti/氧化石墨烯/Ti共格界面模型。采用第一性原理计算方法从电子原子尺度研究了环氧基和羟基对Ti/氧化石墨烯/Ti界面黏附功、界面能、原子结构和电子结构的影响。结果 环氧基和羟基都会使界面黏附功变大,界面能减小,形成结合更强、更稳定的界面,其中环氧基的贡献更大。官能团附近的Ti原子与氧化石墨烯中C原子的结合能力减弱。在形成界面时,氧化石墨烯被还原,环氧基和羟基中的O原子与Ti基体会发生反应生成固溶体,羟基中的H原子可能保持与O原子之间的相互作用,也可能会脱离O原子的束缚与Ti基体有相互作用。结论 当氧化石墨烯和Ti基体形成界面时,氧化石墨烯的官能团会固溶在Ti基体中,抑制界面产物脆性相TiC的产生,石墨烯的片层结构更容易被保留,形成界面结合更好的复合材料。     

利用第一性原理研究Ge:Si电子结构与光学性质

采用基于密度泛函理论的平面渡超软赝势方法和广义梯度近似,计算了掺杂Ge前后单晶Si中Si-Ge键的布居值、键长以及能带结构和态密度.计算结果表明,Ge掺杂后体系晶格常数发生变化,Ge-Si键变长,布居值及带隙宽度减小.还进一步研究了掺杂Ge后的光学性质,掺杂后静态介电常数值与纯Si相比有所增大,且吸收带宽变窄、吸收带边明显红移,并对这些掺杂诱导的材料物性变化进行了解释.     

纳米化3J33钢低温渗氮生成相性能第一性原理表征

采用固溶处理、热轧、冷拔变形和电加热的复合技术实现了3J33马氏体时效钢纳米化,平均晶粒尺寸约为70nm。对纳米化的马氏体时效钢分别在390℃和360℃进行8h脉冲等离子体渗氮,利用XRD、显微硬度计和纳米硬度计对渗氮层生成相和性能进行了测试,并且基于第一性原理对渗氮相的性能进行了表征。结果表明,两个温度下渗层中生成的氮化相分别为γ′-Fe4N和FeN0.076,二者均具有较高的硬度和良好的塑性。计算结果表明,γ′-Fe4N和FeN0.076相中N与Fe原子的成键作用较强,且两相都具有延性。     

Ti-25at%Nb合金β、α''和ω相结构稳定性和弹性性质理论计算

采用赝势平面波方法和广义梯度近似对Ti-25at%Nb合金中不同晶体结构β、α"和ω相的弹性常数、内聚能以及电子结构进行了计算,并结合计算结果对β、α"和ω相的结构稳定性进行了讨论.计算结果表明,Ti-25at%Nb合金中β、α"和ω相均满足其结构弹性稳定性要求,其中α"相的结构稳定性最高,而β相的结构稳定性最低;计算结果同时表明,Ti-25at%Nb合金中ω相具有最高弹性模量,β相则具有最低弹性模量.     

Unravelling the Molecular Origin of Organic Semiconductors with High-Performance Thermoelectric Response

A decisive prerequisite toward systematic development of high-efficiency organic thermoelectric materials is not only thoroughly understanding the microscopic physical processes controlling the performance, but also precisely correlating such processes and the macroscopic properties to the basic chemical structures. Here, by using multiscale first-principles calculations, the interplay among thermoelectric properties, microscopic transport parameters, and molecular structures for the whole family of small-molecule organic thermoelectric materials is rationalized, and general molecular design principles are concurrently formulated. It is unveiled that thermoelectric power factor of a wide variety of molecular semiconductors is directly proportional to a unified quality factor, and high-performance thermoelectric response demands to boost the intermolecular electronic coupling, and to suppress the interaction of electron with lattice vibrations. Furthermore, it is uncovered that extending the π-conjugated backbones along the long axis, and maximizing the networks of intermolecular S···S or C H···π contacts meet the proposed material design rule.     

Effect of cation vacancies on the optical and dielectric properties of KSr2Nb5O15: A first-principles study

Using first-principles calculations, the effect of cation vacancies on the electronic structures and optical characters of KSr₂Nb₅O₁₅ (KSN) lead-free ferroelectrics are investigated. The calculated dielectric properties are demonstrated by the experimental results. The cation vacancies involve K⁺ vacancies (KSN-K), Sr²⁺ vacancies (KSN-Sr), and coexisting K⁺ and Sr²⁺ vacancies (KSN-K&Sr). When these cation vacancies exist in KSN, the unit cell volumes decrease, leading to phase transition from tetragonal to orthorhombic, and the cation vacancies show strong effects on the band gap of KSN, declining by 1.46%-9.46%. The optical properties including the static dielectric constants, refraction, and extinction coefficient of KSN-K, KSN-Sr, and KSN-K&Sr increase more than those of KSN without vacancies, but the reflectivity and loss function decrease. All structures with cation vacancies are mainly refractive in the 0-4 eV photon energy range and are reflective at 5-8 eV. The refractivity increases and reflectivity decreases after vacancies occur. KSN-Sr has the largest static dielectric constant while KSN-K&Sr has the smallest values. The dielectric constant can be adjusted in the range of 25% by controlling the cation vacancies. The calculated dielectric properties are in good agreement with the experimental results. The results pave the way to regulate the optical and dielectric properties of lead-free ferroelectrics by controlling different cation vacancies.     

First-principles study of the thermal properties of Zr2C and Zr2CO

First-principles calculations of lattice thermal conductivities and thermodynamic properties of Zr₂C and Zr₂CO were performed using the quasi-harmonic approximation. Oxygen in the lattice gives Zr₂CO higher bonding strength than Zr₂C. Thus, the mechanical properties of Zr₂C are enhanced when the vacancies in its crystal structure are filled with oxygen. Among the critical parameters that determine the lattice thermal conductivity, Zr₂C has significantly higher Grüneisen parameters, thus Zr₂C has lower lattice thermal conductivity than Zr₂CO. In addition, Zr₂CO has a higher heat capacity and thermal expansion coefficient than Zr₂C at most temperatures. These results indicate that the addition of oxygen has increased the stiffness and thermal conductivity of zirconium carbide that contains a large fraction of carbon vacancies due to the filling of vacancies in the Zr₂C lattice and the formation of Zr–O bonds.     

Cobalt-based coordination polymer as high activity electrocatalyst for oxygen reduction reaction: Catalysis by novel active site CoO4N2

[{Co₃(μ₃-OH)(BTB)₂(BPE)₂}{Co_0.5N(C₅H₅)}] (Co-CP) as a coordination polymer for catalyzing oxygen reduction reaction (ORR) has recently been reported to exhibit high ORR performance because of its novel structural characteristics. Nevertheless, the detailed mechanism remains far from enough. Herein, first-principles study of the ORR process of Co(C₆H₅CO₂)₂(C₅H₅N)₂ is carried out, which is the constructed model of monomeric unit for this compound. Most interestingly, the calculated results uncover that in the second proton transfer step, the active site contributes to the reaction is not only the Co atom, but also the O and N atoms which are directly bonded to the Co atom that construct a novel active site CoO₄N₂. Further analysis of the electronic structure demonstrates that the Co, O, and N atoms in the CoO₄N₂ local structure have participated the electron transfer during the entire ORR process. By analyzing the relative energy changes of whole reaction, it can find that the favorable ORR pathway on the Co(C₆H₅CO₂)₂(C₅H₅N)₂ is the 4e⁻ pathway, and the overpotential of ORR on Co(C₆H₅CO₂)₂(C₅H₅N)₂ is calculated as 0.43 V, which is consistent with experimental observation and lower than that on the Pt(111). Furthermore, the results of first-principles molecular dynamics simulations and density of states (DOS) show that Co(C₆H₅CO₂)₂(C₅H₅N)₂ presents good stability. And it also possesses high anti-poisoning ability to some impurity gases such as CO, NO, and NH₃.     

Ga、N、P、Sb掺杂二维砷烯吸附SO2气体的第一性原理研究

基于第一性原理计算，研究了Ga、N、P、Sb元素分别掺杂本征砷烯材料对SO2气体的吸附特性。结果表明，Ga掺杂的砷烯表现为直接带隙半导体；本征砷烯以及P、Sb掺杂的砷烯对SO2呈较弱的物理吸附，N掺杂的砷烯在4种体系中展现出最大的吸附能，为-0.867 eV，不利于SO2解吸；Ga掺杂的砷烯对SO2具有适中的吸附能，为-0.693 eV，同时，吸附SO2前后带隙值变化最显著（0.957 eV），有望作为高效检测SO2的气敏材料。     

First-principles modeling for optimal design,operation, and integration of energy conversion and storage systems

Energy and electricity consumption is expected to increase in the foreseeable future. Concurrently, sustainability concerns of fossil-based energy resources have motivated the use of renewable and reusable energy resources, and the use of more efficient energy-converting and energy-consuming systems. Consequently, for the past decade, there have been major theoretical and experimental advances in (1) energy generation from renewable and reusable resources and (2) energy-consuming and energy-converting devices. This review article focuses on the recent theoretical advances in renewable energy conversion devices such as photovoltaic and fuel cells, and in energy storage devices such as rechargeable batteries, flow batteries, and supercapacitors. Due to similar chemistry, electrochemistry, and physics of these systems, modeling similarities between different energy systems are highlighted. This review puts into perspective how first-principles mathematical modeling has contributed to systematic advances in the optimal design, operation, and integration of these systems. © 2018 American Institute of Chemical Engineers AIChE J, 65: e16482 2019