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Topological phases in pyrochlore thallium niobateTl2Nb2O6+x(烧绿石结构铌酸铊Tl2Nb2O6+x中的拓扑相)
Wei Zhang,Kaifa Luo, Zhendong Chen,Ziming Zhu, Rui Yu, Chen Fang &Hongming Weng
npj Computational Materials 5:105(2019)
doi:s41524-019-0245-5
Published online:1 November 2019

Abstract| Full Text | PDF OPEN

摘要:新型拓扑电子材料的发现带来了发现新物理的机会。迄今,很多拓扑材料已经由理论提出并被实验验证。可惜的是,拓扑氧化物的存在仍旧缺少令人信服的实验证据。这是因为氧元素的强氧化作用通常会导致离子晶体的形成,使能带反转不太可能出现。另外,在单一材料中实现不同拓扑电子态非常困难,但这对于探索拓扑相变又是急需的。本研究运用第一性原理计算和对称性分析方法,提出在烧绿石结构的Tl2Nb2O6+x0x 1.0)中,氧固溶体在实验上的连续可调会导致多种不同的拓扑电子态。通过改变氧含量和/或调节晶体对称性,可以得到拓扑绝缘体、狄拉克半金属和三重简并点半金属等。当x = 1时,体系是半金属,其费米能级处具有二次型色散接触点。在平面内不同应变的作用下,其会转变为Dirac半金属或者拓扑绝缘体。当x = 0.5时,Tl2Nb2O6.5体系空间反演对称性的自然破缺导致了三重简并点的产生。当x 0时,Tl2Nb2O6成为窄能隙的普通绝缘体。这些由氧的固溶体驱动的拓扑相变是独特的、合乎物理的,其本质是源于T1+Tl3+的价态改变。这种拓扑氧化物将有望用于电子关联引起的拓扑电子态的研究及其潜在应用   

Abstract: discovery of new topological electronic materials brings a chance to uncover new physics. Up to now, many materials have been theoretically proposed and experimentally proved to host different kinds of topological states.Unfortunately, there is little convincing experimental evidence for the existence of topological oxides. The reason is that oxidation of oxygen leads to ionic crystal in general and makes band inversion unlikely. In addition, the realization of different topological states in a single material is quite difficult, but strongly needed for exploring topological phase transitions. In this work, using first-principles calculations and symmetry analysis, we propose that the experimentally tunable continuous solid solution of oxygen in pyrochlore Tl2Nb2O6+x (0x1.0) leads to various topological states. Topological insulator, Dirac semimetal, and triply degenerate nodal point semimetal can be realized in it via changing the oxygen content and/or tuning the crystalline symmetries. When x=1, it is a semimetal with quadratic band touching point at Fermi level. It transits into a Dirac semimetal or a topological insulator depending on the in-plane strain. When x=0.5, the inversion symmetry is spontaneously broken in Tl2Nb2O6.5, leading to triply degenerate nodal points. When x=0, Tl2Nb2O6 becomes a trivial insulator with a narrow band gap. These topological phase transitions driven by solid solution of oxygen are unique and physically plausible due to the variation of valence state of Tl+ and Tl3+. This topological oxide will be promising for studying correlation induced topological states and potential applications. 

Editorial Summary

New topological oxidepromotes the diversity of topological electronic states福建师大张薇联手翁红明、余睿:一窥拓扑电子态万花筒

烧绿石结构的Tl2Nb2O6+x0x 1.0)是氧的固溶体,且具有氧含量在实验上连续可调的特性。本研究报道了此特性使得Tl2Nb2O6+x展现出独特的拓扑相变。福建师范大学的张薇副教授与lovebet爱博体育官方网站物理研究所的翁红明研究员、武汉大学的余睿教授等合作,运用第一性原理计算和对称性分析方法,提出通过调控氧含量及/或晶体对称性,可在Tl2Nb2O6+x体系中实现多种不同的拓扑电子态:包括拓扑绝缘体、狄拉克半金属和三重简并点半金属等。T1价态由+1转变成+3导致了这些拓扑相变的产生。该氧化物系列拓扑性质的研究将有助于关联拓扑电子态的探索及其潜在应用

The pyrochlore Tl2Nb2O6+x (0 x 1.0) is a solid solution of oxygen, whose oxygen content iscontinuously tunable in experiments. This study reported that the solid solution of oxygen led to unique topological phase transitions. Associate Professor Wei Zhang of Fujian Normal University, in collaboration with Professor Hongming Weng at the Institute of Physics, Chinese Academy of Sciences, and Professor Rui Yu from Wuhan University, using first-principles calculations and symmetry analysis, proposedthat a variety of topological electronic states could be achieved in the Tl2Nb2O6+x system,by tuning oxygen content and/or crystal symmetry. These topological electronic states include topological insulator, Dirac semimetal, and triply degenerate nodal point semimetal. The topological phase transitions are due to the T1 valence transition from +1 to +3. The study of the topological oxide will be promising for the exploration of the correlated topological electronic states and potential applications.

Ternary superconducting cophosphorus hydrides stabilized via lithium (通过锂掺杂稳定的三元超导磷氢化合物)
Ziji Shao, Defang Duan, Yanbin Ma, Hongyu Yu, Hao Song, Hui Xie, Da Li, Fubo Tian, Bingbing Liu & Tian Cui
npj Computational Materials 5:104(2019)
doi:s41524-019-0244-6
Published online:30 October 2019

Abstract| Full Text | PDF OPEN

摘要:受高压下硫化氢200 K超导电性和磷化氢复杂结构相变的启发,本研究将第一性原理计算与晶体结构预测技术相结合,探索高压下Li-P-H三元化合物的稳定结构,以期发现新型高温超导体。研究发现在P-H体系中通过掺杂锂元素可以使得磷氢化合物在高压下稳定,在100300 GPa的压力范围内,发现了四个稳定存在的化合物LiPH3LiPH4LiPH6LiPH7。尤其值得关注的是,理论预测具有对称性的原子相LiPH6是潜在的高温超导体,在200 GPa时超导转变温度为150-167 K,并且随着压力的增加超导转变温度降低。除了-LiPH6是离子型原子相外,其余三个稳定存在的三元氢化物中都包含PH共价框架,而离子锂分布在框架周围。本研究工作还提出了合成三元锂磷氢化物的一种可能路径:LiP + H2LiPHn,为将来的高压合成实验提供了有益和明确的指导,并为三元超导氢化物的进一步探索提供了参考   

Abstract:Inspired by the diverse properties of sulfur hydrides and phosphorus hydrides, we combine first-principles calculations with structure prediction to search for stable structures of LiPH ternary compounds at high pressures with the aim of finding novel superconductors. It is found that phosphorus hydrides can be stabilized under pressure via additional doped lithium. Four stable stoichiometries LiPH3, LiPH4, LiPH6, and LiPH7 are uncovered in the pressure range of 100–300 GPa. Notably, we find an atomic LiPH6 with symmetry which is predicted to be a potential high-temperature superconductor with a Tc value of 150–167K at 200GPa and the Tc decreases upon compression. All the predicted stable ternary hydrides contain the P–H covalent frameworks with ionic lithium staying beside, but not for –LiPH6. We proposed a possible synthesis route for ternary lithium phosphorus hydrides: LiP+H2→LiPHn, which could provide helpful and clear guidance to further experimental studies. Our work may provide some advice on further investigations on ternary superconductive hydrides at high pressure. 

Editorial Summary

Conventional high-temperature superconductors:  lithium-doped phosphorus hydrides吉林大学预测传统高温超导体:锂掺杂磷氢化合物

该研究工作预测了一种新型的三元传统高温超导体LiPH6,该材料在200万大气压的高压下超导转变温度可达167 K,远高于液氮温度(77 K)。来自吉林大学物理学院的崔田教授/段德芳副教授课题组,通过第一性原理计算结合晶体结构搜索技术,预测了一系列高压下稳定存在的三元氢化物LiPH3LiPH4LiPH6LiPH7,这类材料是由Li掺杂二元磷氢化合物形成的。母体氢化物P-H体系在高压下不稳定,会分解为单质PH2,而引入额外的电子可以稳定P-H体系,在高压下形成稳定的三元化合物。其中超导性质最为突出的是LiPH6,在200万大气压的压力下超导转变温度可达167 K。该研究工作还提出了合成三元锂磷氢化合物的一种可能路径:LiP + H2→LiPHn,为高压下三元氢化物超导材料的深入研究提供了重要参考

In this study, a new conventional high temperature superconductor LiPH6 is predicted. The critical temperature Tof this material is calculated to be 167 K at 200 GPa, which is much higher than liquid nitrogen temperature (77 K). The research group of Professor Tian Cui/ Associate Professor Defang Duan from the College of Physics of Jilin University, predicted a series of stable ternary hydrides LiPH3, LiPH4, LiPHand LiPH7 under high pressure by means of first-principles calculations and structure prediction. These materials can be formed through doping lithium in binary phosphorus hydrides. The host P-H system is unstable under high pressure and will decompose into elemental P and H2. The introduction of additional electrons stabilizes the P-H system and form a series of stable ternary compounds at high pressure. Notably, an atomic LiPH6 with symmetry which is predicted to be a potential high-temperature superconductor with aTvalue of 150–167K at 200GPa. In addition, the research also proposed a possible synthesis route for ternary lithium phosphorus hydrides: LiP+H2→LiPHn, which could provide helpful and clear guidance to further experimental studies. This work may provide some advice on further investigations on ternary superconductive hydrides at high pressure.

Tensorial stress-strain fields and large elastoplasticity as well as friction in diamond anvil cell up to 400GPa (承受400 GPa的金刚石砧座单元:拉伸应力-应变场、大弹性塑性和摩擦)
Valery I. LevitasMehdi Kamrani & Biao Feng
npj Computational Materials 5:94(2019)
doi:s41524-019-0234-8
Published online:1 October 2019

Abstract| Full Text | PDF OPEN

摘要:在极端压力下金刚石砧座单元中的各种现象(断裂、相变和化学反应)都受到应力和塑性应变张量所有分量场的强烈影响。然而,它们却无法测量。本研究提出一种实验-理论-计算耦合的测量方法,允许(使用已公开的实验数据)优化、校准和验证高达400 GPa的钨(W)和金刚石弹塑性行为模型和接触摩擦模型,并重建W和金刚石中所有应力分量和大塑性应变张量。尽管人们已普遍接受了应变引起的各向异性、应变硬化和路径依赖的可塑性,但本研究表明,大塑性应变后的W表现为各向同性、完美塑性和独立于路径的完美塑性表面。此外,即使在如此大的场梯度中,也发现了弹塑性特性的尺度非依赖性。本研究结果为定量极端应力科学和创纪录高压打开了新的机遇   

Abstract:Various phenomena (fracture, phase transformations, and chemical reactions) studied under extreme pressures in diamond anvil cell are strongly affected by fields of all components of stress and plastic strain tensors. However, they could not be measured. Here, we suggest a coupled experimental theoretical computational approach that allowed us (using published experimental data) to refine, calibrate, and verify models for elastoplastic behavior and contact friction for tungsten (W) and diamond up to 400GPa and reconstruct fields of all components of stress and large plastic strain tensors in W and diamond. Despite the generally accepted strain-induced anisotropy, strain hardening, and path-dependent plasticity, here we showed that W after large plastic strains behaves as isotropic and perfectly plastic with path-independent surface of perfect plasticity. Moreover, scale-independence of elastoplastic properties is found even for such large field gradients. Obtained results open opportunities for quantitative extreme stress science and reaching record high pressures. 

Editorial Summary

Diamond anvil cell: tensorial stress-strain fields, large elastoplasticity and friction揽瓷器活的金刚砧:需要承受多少委屈?

静态高压研究中,兆伏压力是由金刚砧座单元中的两颗金刚石对稀薄样品的压缩而产生的。但金刚砧所受的应力和塑性应变张量却无法测量。该研究提出了一种新颖的实验-理论-计算耦合的测试方法,这一方法可使用已知实验数据来构建模型,从而提取有关弹塑性和摩擦方式的完整信息,以及金刚砧单元(diamond anvil cells)中的材料在受极端压力时的各种复杂张量场的完整信息。来自美国爱荷华州立大学航空航天工程和机械工程系的Valery I. Levitas教授团队,优化、校准和验证了任意样品的弹塑性行为模型及钨(W)样品可高达400 GPa的接触摩擦,重建了W和金刚石中的应力和大塑性应变张量的所有分量场。该研究除了获取屈服强度和摩擦的压力依赖性定量信息、高阶弹性常数的定量信息外,还揭示了极大应变和压力下,弹塑性行为的一些共同特性:1)尽管人们已普遍认定应变会导致各向异性、应变硬化和路径相关的塑性,但大塑性应变之后的W却表现为各向同性,且未表现出应变硬化和路径依赖。2)尽管样品厚度达μm级、应力可达5 GPa /μm和塑性应变梯度巨大,但样品的弹塑性特性却具有非尺度依赖性。这两种性能都极大地简化了可塑性理论和极端条件下的测量。该研究在塑性方面的发现还暗示了在这种极端载荷下塑性摩擦的重要特性:塑性摩擦与塑性应变、塑性应变路径和尺寸毫无关联

A novel coupled experimental theoretical computational approach is suggested, which allowed to extract complete information about elastoplastic properties and friction rules, as well as all complex tensorial fields using known experimental data for materials compressed in a diamond anvil cells under extreme pressure. A team led by Prof. Valery I. Levitas from the Departments of Aerospace Engineering and Mechanical Engineering, Iowa State University, USA, refined, calibrated, and verified models for elastoplastic behavior of a sample and contact friction for W up to 400GPa and reconstruct fields of all components of stress and large plastic strain tensors in W and diamond. In addition to quantitative information on the pressure dependence of the yield strength and friction, as well as higher-order elastic constants, they justifed some general unique properties of elastoplastic behavior under very large strains and pressures: (a) Despite the generally accepted strain-induced anisotropy, strain hardening, and path-dependent plasticity, W after large plastic strains behaves isotropically and does not exhibit strain hardening and path dependence. (b) Despite the μm-sized sample thickness and huge stress (5GPa/μm) and plastic strain gradients, scale-independence of elastoplastic properties is found. Both of these properties drastically simplify plasticity theory and measurements under extreme conditions. Their finding for plasticity also implies important properties for plastic friction under such extreme loading: Plastic friction is plastic strain-, plastic strain path-, and scale-independent.

Interpretable deep learning for guided microstructure-property explorations in photovoltaics (基于可解释性深度学习探索光伏引导性微结构-性能)
Balaji Sesha Sarath PokuriSambuddha GhosalApurva KokateSoumik Sarkar & Baskar Ganapathysubramanian
npj Computational Materials 5:95(2019)
doi:s41524-019-0231-y
Published online:1 October 2019

Abstract| Full Text | PDF OPEN

摘要:微观结构决定了薄膜有机半导体膜的光伏性能。微观结构与宏观性能之间的构效关系通常呈高度非线性化,其评估成本很高,因此微观结构的优化具有相当大的挑战性。本研究展示了一种数据驱动的方法,使用深度卷积神经网络将微观结构映射到光伏性能。lovebet爱博体育官方网站用两个关键指标来表征这一方法:可泛化性(是否学到了一个合理的映射?)和可解释性(能否产生有意义的微观结构特征来帮助其预测?)。同时具又这两个关键指标的替代模型对于后续的设计和开发是非常有价值的。lovebet爱博体育官方网站通过使用替代模型来说明这一点,该模型用于手动探索(验证已知领域的洞察力)和微观结构的自动优化。lovebet爱博体育官方网站认为这样的方法将可广泛应用于各种对微结构敏感的设计问题   

Abstract:The microstructure determines the photovoltaic performance of a thin film organic semiconductor film. The relationship between microstructure and performance is usually highly non-linear and expensive to evaluate, thus making microstructure optimization challenging. Here, we show a data-driven approach for mapping the microstructure to photovoltaic performance using deep convolutional neural networks. We characterize this approach in terms of two critical metrics, its generalizability (has it learnt a reasonable map?), and its intepretability (can it produce meaningful microstructure characteristics that influence its prediction?). A surrogate model that exhibits these two features of generalizability and intepretability is particularly useful for subsequent design exploration. We illustrate this by using the surrogate model for both manual exploration (that verifies known domain insight) as well as automated microstructure optimization. We envision such approaches to be widely applicable to a wide variety of microstructure-sensitive design problems. 

Editorial Summary

Interpretable deep learning: microstructure-property explorations名字与火车一样长的教授等:微结构-大性能的玩法

该研究利用卷积神经网络(CNN)的多功能性,将薄膜有机光伏(OPV)的活性层形态映射到性能指标——短路电流Jsc。来自美国爱荷华州立大学机械工程系的Soumik Sarkar教授和Baskar Ganapathysubramanian(这个姓恰好20字母)教授等,训练了一种形态分类器,可将OPV形态和短路电流关联到一起。他们测试了几种深度和宽度不同的学习框架,这些学习框架可以从给定的一组形态及其标签中学习,最后的结果发现该学习框架具有很高的准确性和F1得分。为了区分这些同样表现良好的模型并对它们进行排序,作者使用了两个额外的附加度量。首先是揭示习得的结构-性质关系的概括性。他们确定了网络架构,可以用可用的数据集概括地图,并根据“将未看到的形态投射到已学习过的分布上”的能力进行量化,并做出了良好的预测。其次是可解释性。这是理解工程系统行为的相当重要的指标。他们引入了一种称为DLSP(结构属性查询深度学习)的方法,用于从数据中学习结构-性能之间的构效关系。作者认为这种方法可广泛应用于各种对微结构敏感的设计问题

Versatility of Convolutional Neural Networks (CNN) is reported to map the active layer morphology of thin film organic photovoltaics (OPV) to a performance metric, the short-circuit current Jsc. A team co-led by Prof. Soumik Sarkar and Prof. Baskar Ganapathysubramanian from the Department of Mechanical Engineering, Iowa State University, USA, trained a morphology classifier that maps an OPVmorphology to a short-circuit current.They tested several architectures (of varying depth and width) that can learn from a given set of morphologies and their labels, and demonstrated very high accuracy, and F1 score. To distinguish and rank order between these equally well performing models, the authors used two additional measures. The first is generalizability to reveal the learnt structure-property relationship. They identified network architectures that can generalize the map with the available dataset and quantify in terms of the ability to ‘project the unseen’ morphology onto the learnt distribution and made good predictions.The second is interpretability, a fairlyimportant metric for understanding the behavior of engineered systems.They introduced an approach called DLSP (Deep Learning for Structure Property interrogation) for learning the structure-property relationship from data. The authorsenvision such approaches to be widely applicable to a wide variety of microstructure-sensitive design problems.

Higher-order topological solitonic insulators (基于磁孤子的高阶拓扑绝缘体)
Zhixiong Li, Yunshan Cao, Peng Yan & Xiangrong Wang
npj Computational Materials 5:107(2019)
doi:s41524-019-0246-4
Published online:12 November 2019

Abstract| Full Text | PDF OPEN

摘要:在各类系统中寻找并发现拓扑相和拓扑材料是当前物质科学及材料工程领域的一个核心问题。最近的声学和光学实验均观察到了二阶拓扑边界态(角态)。受此启发,lovebet爱博体育官方网站研究了磁孤子阵列的集体回旋振荡运动,这些磁孤子通过磁偶极相互作用耦合在一起,组成二维呼吸型kagome晶格。lovebet爱博体育官方网站理论计算了系统的相图,并发现:当两种晶格常数之比大于某一临界值时,系统中会出现平凡的一阶Tamm-Shockley边界态和非平凡的二阶拓扑角态。lovebet爱博体育官方网站进一步证实,这些新出现的角态在结构缺陷和强度适当的无序下都表现出优异的拓扑稳定性。微磁模拟结果很好的证实了理论预测。lovebet爱博体育官方网站的结果为研究基于磁孤子的高阶拓扑绝缘体铺平了道路   

Abstract:Pursuing topological phase and matter in a variety of systems is one central issue in current physical sciences and engineering. Motivated by the recent experimental observation of corner states in acoustic and photonic structures, we theoretically study the dipolar-coupled gyration motion of magnetic solitons on the two-dimensional breathing kagome lattice. We calculate the phase diagram and predict both the Tamm-Shockley edge modes and the second-order corner states when the ratio between alternate lattice constants is greater than a critical value. We show that the emerging corner states are topologically robust against both structure defects and moderate disorders. Micromagnetic simulations are implemented to verify the theoretical predictions with an excellent agreement. Our results pave the way for investigating higher-order topological insulators based on magnetic solitons. 

Editorial Summary

Higher-order topological insulator: Corner states emerging from the collective oscillation of magnetic vortices电子科技大学揭示:磁涡旋集体振荡涌现拓扑角态

本研究提供了在磁性系统中实现高阶拓扑绝缘相的方法,在磁孤子阵列中发现了拓扑稳定的角态来自电子科技大学的严鹏教授领导的团队,报道了一种基于磁涡旋的呼吸型kagome晶格,可以实现高阶拓扑绝缘相(角态),通过调节两种晶格常数的比值,系统可以在普通绝缘相和高阶拓扑绝缘相之间转变。观察到的角态模式不受系统缺陷和无序的干扰,能保持很好的拓扑稳定性。该研究结果为磁性系统中实现高阶拓扑绝缘体开辟了道路,并将激励实验专家们在当前技术条件下对这种新奇拓扑态进行观测

This study provides a method to realize the higher-order topological insulating phase in magnetic system, and finds the topologically stable corner states based on magnetic solitons. A team led by Professor Peng Yan from the University of Electronic Science and technology of China, reported a kind of breathing kagome lattice based on magnetic vortices to support the higher-order topological insulating state (corner state). By adjusting the ratio of two different lattice constants, one can realize the phase transition between trivial insulating phase and higher-order topological phase. The emerging corner states are topologically robust against both structure defects and moderate disorders. These findings pave the way for the realization of higher-order topological insulator in magnetic system and shall encourage experimentalists to detect them within current technology reach.

De novo exploration and self-guided learning of potential-energy surfaces (势能面的从头探索和自导学习)
Noam BernsteinGabor Csanyi & Volker L. Deringer
npj Computational Materials 5:99(2019)
doi:s41524-019-0236-6
Published online:11 October 2019

Abstract| Full Text | PDF OPEN

摘要:基于机器学习(ML)的原子间势模型作为材料模拟的工具正在迅速发展。然而,由于它们的灵活性,它们需要大型拟合数据库,而这些数据库通常是通过大量手动选择和人工调优的方式来创建的。本研究显示,ML原子间势可以以一种高度自动化的方式构建,并从一开始(从头开始)就在同一个协议中探索和拟合不同的势能面。关键的启用步骤是使用构型均质化的内核度量,它允许在每个步骤中选择几个最相关和最多样化的结构。尽管只需要在小单元上进行相对少量的单点DFT计算,但所获得的ML原子间势对结构搜索过程中出现的各种空间构型的预测都准确而可靠。lovebet爱博体育官方网站将该方法应用于具有不同化学性质和配位环境材料中,这标志着在物理、化学和材料科学中,ML原子间势向着更加常规的应用迈开了重要一步   

Abstract:Interatomic potential models based on machine learning (ML) are rapidly developing as tools for material simulations. However, because of their flexibility, they require large fitting databases that are normally created with substantial manual selection and tuning of reference configurations. Here, we show that ML potentials can be built in a largely automated fashion, exploring and fitting potential-energy surfaces from the beginning (de novo) within one and the same protocol.The key enabling step is the use of a configuration-averaged kernel metric that allows one to select the few most relevant and diverse structures at each step.The resulting potentials are accurate and robust for the wide range of configurations that occur during structure searching, despite only requiring a relatively small number of single-point DFT calculations on small unit cells.We apply the method to materials with diverse chemical nature and coordination environments, marking an important step toward the more routine application of ML potentials in physics, chemistry, and materials science. 

Editorial Summary

De novo exploration and self-guided learning of potential-energy surfaces势能面:从头探索和自导学习

该研究提出了一种高效且统一的方法,用于生成拟合机器学习(ML)原子间势的参考数据库,从而一开始就通过ML驱动的搜索和相似性度量来探索构型空间,所有这些都不需事先知道哪些结构是相关或不相关的。由英国剑桥大学工程系和牛津大学化学系的Volker L. Deringer教授领导的研究小组揭示,ML原子间势可以以一种高度自动化的方式构建,并从一开始(从头开始)在同一协议中探索和拟合不同的势能面。与连续的主动学习相反,它们的目标是收敛并形成一个合理的势函数,即在无需额外拟合的情况下,这些势函数可以描述好各种构型。作者证明了该方法可以描述好从石墨片到密排过渡金属等多种结构和化合物。这项研究工作为计算机如何如何仅基于数据和相似性测量来获得结构化学提供了概念性的认知,并为在材料发现中更常规地应用ML势函数铺平了道路

An efficient and unified approach for generating reference databases for fitting machine learning (ML) potentials is presented to explore structural space from the beginning (de novo) by ML-driven searching and similarity measures, all without any prior knowledge of what structures are or are not relevant. A research group led by Prof. Volker L. Deringer from the Department of Engineering, University of Cambridge, and the Department of Chemistry, University of Oxford, UK, displayed that ML potentials can be built in a largely automated fashion, exploring and fitting potential-energy surfaces from the beginning (de novo) within one and the same protocol.In contrast with continuous active learning, their aim is to converge to a potential that can describe a wide range of configurations without the need for additional fitting.They demonstrate the ability to cover a broad range of structures and chemistries, from graphite sheets to a densely packed transition metal.Their work provides conceptual insight into how computers can discover structural chemistry based on data and similarity measures alone, and it paves the way for a more routine application of ML potentials in material discoveries.

Creating multiferroic and conductive domain walls in common ferroelastic compounds (在普通铁弹性化合物中创建多铁性和导电性畴壁)
Hong Jian Zhao & Jorge íniguez
npj Computational Materials 5:92(2019)
doi:s41524-019-0229-5
Published online:12 September 2019

Abstract| Full Text | PDF OPEN

摘要:铁电体和铁弹体中的畴壁通常表现出特殊的功能特性,为纳米器件的设计提供了有趣的途径。本研究使用第一原理模拟阐释一种处理此类畴壁的方法,该方法要与典型的铁弹性钙钛矿LaGaO3 CaTiO3(绝缘、非磁性、非极性)一起使用。lovebet爱博体育官方网站的研究表明,可以使用各种取代掺杂剂来创建局限在这些化合物畴壁内的长程有序结构,从而产生具有量身定制性能的功能性界面。因此,lovebet爱博体育官方网站在绝缘基质内确定了制备金属畴壁的清晰策略。此外,lovebet爱博体育官方网站找到了创建具有同样铁电有序(正常或不正常)的磁性畴壁的方法,从而为获得磁电多铁提供了原创性方法。鉴于钙钛矿薄膜中高密度畴结构制备的最新进展,lovebet爱博体育官方网站的结果提示了通往新型功能纳米材料的明确道路   

Abstract:Domain walls in ferroelectrics and ferroelastics often present peculiar functional properties, offering an intriguing route toward the design of nano-devices. Here we use first-principles simulations to illustrate an approach for engineering such walls, working with representative ferroelastic perovskites LaGaO3 and CaTiO3 (insulating, non-magnetic, non-polar). We show that a wide range of substitutional dopants can be used to create long-range-ordered structures confined within the walls of these compounds, yielding functional interfaces with tailor-made properties. We thus identify clear-cut strategies to produce metallic walls within an insulating matrix. Further, we find ways to create magnetic walls that also display ferroelectric order (proper or improper), thus providing an original route to obtain magnetoelectric multiferroics. Given the recent developments on the preparation of high-density domain structures in perovskite films, our results suggest a definite path toward new functional nano-materials. 

Editorial Summary

Common ferroelastic compounds: Create multiferroic-conductive domain walls铁弹材料的麻袋:要绣多铁性-导电畴壁之花?

该研究使用化学掺杂方法在普通铁弹性材料的畴壁上创建了功能界面。来自卢森堡科学技术学院材料研究与技术部(LIST)的Hong Jian Zhao Jorge íniguez教授,基于密度泛函理论(DFT)的第一性原理方法,揭示了由不同掺杂剂引起的一些有关畴壁功能的规律,用于指导畴壁的设计。如,3d掺杂剂倾向于提供绝缘溶体,而4d5d元素会产生导电壁。同样,他们观察到较小的原子(TiVCr)会在畴壁处产生正常的铁电有序;相反,较大的畴壁则驻留在更对称的构型中,因此相应的(铁弹性)畴壁不太可能出现极性。他们的研究结果为此类材料设计策略提供了充足的支持,预测了多种掺杂剂的长距离取代的自发出现。此外,他们确定了具有所需各种重要特性(包括电导率和磁电多铁性)畴壁的具体策略

Functional interfaces at domain walls of common ferroelastic materials is created by chemical doping. Hong Jian Zhao and Jorge íniguez from the Materials Research and Technology Department, Luxembourg Institute of Science and Technology (LIST), Luxembourg, using first-principles methods based on density functional theory (DFT), suggested a few trends regarding the DW functionality that can be induced by different dopants, which can be used as guidelines for DW design. For example, they found that 3d dopants tend to render insulating solutions, which 4d and 5d elements yield conductive walls. Also, they observed that smaller atoms (Ti, V, Cr) result in proper ferroelectric order at the domain walls; in contrast, bigger ones remain in more symmetric configurations, so that the polarity of the corresponding (ferroelastic) walls is improper. Their research provided ample support for this materials-design strategy, predicting the spontaneous occurrence of long-range-ordered substitutions for a large variety of dopants. Further, they identified specific strategies to obtain walls with all-important properties, including conductivity and magnetoelectric multiferroism.

Unavoidable disorder and entropy in multi-component systems (多组分系统中不可避免的无序和熵)
Cormac ToherCorey OsesDavid Hicks & Stefano Curtarolo
npj Computational Materials 5:69(2019)
doi:s41524-019-0206-z
Published online:10 July 2019

Abstract| Full Text | PDF OPEN

摘要:对改进材料功能的更高需求正在推动人们寻找更复杂的多组分材料。尽管材料的组分空间有所增加,但含有四种或四种以上的有序化合物是很罕见的。本研究通过对AFLOW数据库的统计分析,揭示了焓和熵的增加与化合物数量的增加之间的竞争关系。在熵增益超过焓增益时,就会在物质的数目上找到一个临界值。一旦超过该值,焓可忽略不计,而完全无序或部分无序将不可避免地出现   

Abstract:The need for improved functionalities is driving the search for more complicated multi-component materials. Despite the factorially increasing composition space, ordered compounds with four or more species are rare. Here, we unveil the competition between the gain in enthalpy and entropy with increasing number of species by statistical analysis of the AFLOW data repositories. A threshold in the number of species is found where entropy gain exceeds enthalpy gain. Beyond that, enthalpy can be neglected, and disorder—complete or partial—is unavoidable. 

Editorial Summary

Multi-component systems: Unavoidable disorder and entropy想煮一锅有序的八宝粥:可能门都没有

当晶体的性能无太多显著特点时,其无序体系可能拥有更加良好的性能,这将为技术的革新带来希望。由美国杜克大学机械工程与材料科学系的Stefano Curtarolo领导的研究小组,介绍了他们理论探索的成果。他们认为他们需要通过新颖的思路去探寻新材料。(I)用焓优化方法来搜索多组分系统是徒劳的。随着化合物数量N的增加,发现新材料的概率将会下降,而即使找到有序的材料,它也会被诸多无序结构覆盖。高熵促进发生在4种混合物态中(或~5 +不同的化学键中)。(II)低温下的迟滞动力学可能是件好事。无序是难以避免的,高温合成的高熵固溶体可以在低温相分离中保存下来,同时提供有价值的应用技术。(IIIMaddox的诅咒只是一个通常的情况。这实际上是件好事,因为它需要强制统计分析焓与熵的相互作用。无序体系的建模不能再因为困难和麻烦而被忽视了。复杂多组分材料的研究必将由包含无序的体系来带动,无序是不可避免和不可忽略的

Disordered systems can lead to remarkable properties—unexpected from the homologous crystalline counterparts—enabling revolutionary technologies. A research group led by Stefano Curtarolo from the Department of Mechanical Engineering and Materials Science, Duke University, USA, introduced the achievement of their theoretical exploration. They believed that they just need to search for materials with a different mindset. (I) The search for multi-component systems, performed with enthalpy optimization, is futile. With increasing N (the number of species), the discovery probability decreases, and, even if an ordered material is found, it would be overwhelmed by engulfing disorder. High-entropy promotion occurs at ~4 mixing species (~5+ with different bond types). (II) Sluggish kinetics at low temperatures can be a blessing. Disorder is hard to cure, and high entropy solid-solutions synthesized at high-temperature can survive low-temperature phase separation while providing valuable technological applications. (III) Maddox’s scandal was only an apparent curse. It was actually a blessing as it forced statistical analysis of the enthalpy versus entropy interplay.  Modeling can no longer ignore disorder—often neglected due to compelling difficulties. Advances in complex multi-component materials research will be driven by embracing disorder. It is unavoidable.

The study of magnetic topological semimetals by first principles calculations (磁性拓扑半金属的第一性原理计算研究)
Jinyu ZouZhuoran He & Gang Xu
npj Computational Materials 5:96(2019)
doi:s41524-019-0237-5
Published online:04 October 2019

Abstract| Full Text | PDF OPEN

摘要:磁性拓扑半金属是一种时间反演破缺,在费米面附近具有孤立简并点或简并线的拓扑量子材料。其典型的拓扑性质是体-边界对应,即在表面具有费米弧或鼓膜态。根据简并度及其在动量空间的分布特点,拓扑半金属一般分为外尔半金属,狄拉克半金属,节点线半金属,三重简并点半金属等。在本篇综述中,lovebet爱博体育官方网站从第一性原理计算的角度介绍了近年来磁性拓扑半金属的进展。首先回顾了早期预言的磁性外尔半金属如烧绿石铱氧化物和HgCr2Se4,以及最近提出的Heusler化合物,Kagome层状材料,蜂巢格子等。其次讨论了磁性狄拉克半金属的最新进展,特别是受第三类磁空间群保护的CuMnAs和受第四类磁空间群保护的EuCd2As2。之后介绍了包含自旋轨道耦合效应并稳定的磁性节点线半金属Fe3GeTe2LaClLaBr)。最后,lovebet爱博体育官方网站展望了磁性拓扑半金属未来的发展和研究方向   

Abstract:Magnetic topological semimetals (TSMs) are topological quantum materials with broken time-reversal symmetry (TRS) and isolated nodal points or lines near the Fermi level. Their topological properties would typically reveal from the bulk-edge correspondence principle as nontrivial surface states such as Fermi arcs or drumhead states, etc. Depending on the degeneracies and distribution of the nodes in the crystal momentum space, TSMs are usually classified into Weyl semimetals (WSMs), Dirac semimetals (DSMs), nodal-line semimetals (NLSMs), triple-point semimetals (TPSMs), etc. In this review article, we present the recent advances of magnetic TSMs from a computational perspective. We first review the early predicted magnetic WSMs such as pyrochlore iridates and HgCr2Se4, as well as the recently proposed Heusler, Kagome layers, and honeycomb lattice WSMs. Then we discuss the recent developments of magnetic DSMs, especially CuMnAs in Type-III and EuCd2As2 in Type-IV magnetic space groups (MSGs). Then we introduce some magnetic NLSMs that are robust against spin–orbit coupling (SOC), namely Fe3GeTe2 and LaCl (LaBr). Finally, we discuss the prospects of magnetic TSMs and the interesting directions for future research. 

Editorial Summary

Magnetic Topological Semimetal Materials磁性拓扑半金属材料

本篇综述介绍了近年来在磁性拓扑半金属材料预测方面的进展。来自华中科技大学的徐刚研究组从磁性空间群与第一性原理计算的角度,纵览了磁性拓扑半金属包括外尔半金属、狄拉克半金属和节点线半金属材料预测和设计的最新进展。他们首先回顾了早期预言的磁性外尔半金属如烧绿石铱氧化物和HgCr2Se4,以及最近提出的Heusler化合物,Kagome层状材料,蜂巢格子等;其次讨论了受第三类磁空间群保护的CuMnAs和受第四类磁空间群保护的EuCd2As2两种磁性狄拉克半金属;然后介绍了在自旋轨道耦合作用下依然稳定的磁性节点线半金属Fe3GeTe2LaClLaBr)。最后展望了磁性拓扑半金属未来的发展和研究方向

This article reviewed the recently prospected magnetic topological semimetal (MTSM) materials. A team led by Gang Xu from Huazhong University of Science and Technology, presented the recent advances of MTSMs including Weyl semimetals (WSMs), Dirac semimetals (DSMs) and nodal-line semimetals (NLSMs), from the perspective of magnetic space group and first principles calculations. They firstly reviewed the early predicted magnetic WSMs such as pyrochlore iridates and HgCr2Se4, as well as the recently proposed Heusler, Kagome layers, and honeycomb lattice WSMs. Then they discussed the recent developments of magnetic DSMs, especially CuMnAs in Type-III and EuCd2As2 in Type-IV magnetic space groups (MSGs). Then they introduced some magnetic NLSMs that are robust against spin–orbit coupling (SOC), namely Fe3GeTe2 and LaCl (LaBr). Finally, they also discussed the prospects of magnetic TSMs and the interesting directions for future research.

Strong phonon localization in PbTe with dislocations and large deviation to Matthiessen’s rule (含位错结构的PbTe材料中声子的强局域化振动和马西森定律的大偏差)
Yandong Sun, Yanguang Zhou, Jian Han, Wei Liu, Cewen Nan, Yuanhua Lin, Ming Hu and Ben Xu
npj Computational Materials 5:97(2019)
doi:s41524-019-0232-x
Published online:04 October 2019

Abstract| Full Text | PDF OPEN

摘要:位错可以显著降低材料的热导率进而提高热电材料的品质因子。但是不同能量的声子通过单个位错结构时的行为变化却不为人知。本文中lovebet爱博体育官方网站使用非平衡分子动力学方法,通过消除边界散射以及位错直接相互作用的影响,研究了PbTe中位错和声子的散射。lovebet爱博体育官方网站获得了频率分布热流,声子本征振动模式以及频率分布声子平均自由程。具有1015m-2位错密度的PbTe材料的热导率下降了62%。含位错PbTe中声子的强局域化振动被证实。并且,通过对比lovebet爱博体育官方网站计算得到的声子平均自由程和传统理论模型的结果,lovebet爱博体育官方网站发现传统的理论模型不能够描述全频率空间声子的散射行为,与熟知的马西森规则有很大的偏差。lovebet爱博体育官方网站的结果为发展基于PbTe的热电材料提供了重要的指导,并且为通过位错来提高热电材料性能提供了新思路   

Abstract:Dislocations can greatly enhance the figure of merit of thermoelectric materials by prominently reducing thermal conductivity. However, the evolution of phonon modes with different energies when they propagate through a single dislocation is unknown. Here we perform non-equilibrium molecular dynamics simulation to study phonon transport in PbTe crystal with dislocations by
excluding boundary scattering and strain coupling effect. The frequency-dependent heat flux, phonon mode analysis, and frequency-dependent phonon mean free paths (MFPs) are presented. The thermal conductivity of PbTe with dislocation density on the order of 1015m-2 is decreased by 62%. We provide solid evidence of strong localization of phonon modes in dislocation sample. Moreover, by comparing the frequency-dependent phonon MFPs between atomistic modeling and traditional theory, it is found that the conventional theories are inadequate to describe the phonon behavior throughout the full phonon spectrum, and large deviation to the well-known semi-classical Matthiessen’s rule is observed. These results provide insightful guidance for the development of PbTe based thermoelectrics and shed light on new routes for enhancing the performance of existing thermoelectrics by incorporating dislocations
.
 

Editorial Summary

Molecular Dynamic Simulation : Preliminary Exploration of the Phonon Dislocation Scattering分子动力学模拟:位错声子散射初探

本文研究了明星热电材料PbTe中位错对于声子的散射,发现位错通过使声子振动局域化加强来散射声子,可以极大降低材料的热导率。来自清华大学材料学院的徐贲老师、美国南卡罗莱纳大学胡明老师领导的团队老师,使用非平衡分子动力学方法研究了PbTe中单个位错和声子的散射过程,计算结果表明PbTe4 × 1015 m-2密度的位错导致其热导率下降了62%;通过截面频谱热流分析,获得了PbTe中被位错散射声子的频率;通过拟合得到PbTe声子的平均自由程并且和传统理论结果对比,发现了理论结果的不足之处。创新之处在于,他们的研究消除了边界散射和位错之间互相作用两个因素的干扰,获得位错对于声子的真实散射强度。研究的结果对于通过引入位错调控热电材料热导率具有重要的指导意义。研究由清华大学博士生孙彦东与加州大学洛杉矶分校周彦光共同展开

The phonon-dislocation scattering in PbTe which is the most famous thermoelectric materials has been studied. The dislocations can greatly reduce the thermal conductivity by scattering the phonons to be more localized. A team led by Prof. Ben Xu from Tsinghua University studies the phonon dislocation scattering process in PbTe using non-equilibrium molecular dynamics simulation. They show that a 4 × 1015 m-2 denstiy dislocation can lead to the thermal conductivity decrease for 62%. The frequencies of the phonons most likely been scattered by the dislocation are obtained. The phonon mean free paths (MFPs) are presented and been compared with the traditional theory. It is found that the conventional theories are inadequate to describe the phonon behavior throughout the full phonon spectrum. The innovation in their study is that they eliminate the phonon scattering from boundary and the strain coupling, and obtain a real phonon-dislocation scattering rate. These results provide insightful guidance for the development of PbTe based thermoelectrics and shed light on new routes for enhancing the performance of existing thermoelectrics by incorporating dislocations.

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