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  《npj 计算材料学》是在线出版、完全开放获取的国际学术期刊。发表结合计算模拟与设计的材料学一流的研究成果。本刊由中国科学院上海硅酸盐研究所与英国自然出版集团(Nature Publishing Group,NPG)以伙伴关系合作出版。
  主编为陈龙庆博士,美国宾州大学材料科学与工程系、工程科学与力学系、数学系的杰出教授。
  共同主编为陈立东研究员,中国科学院上海硅酸盐研究所研究员高性能陶瓷与超微结构国家重点实验室主任。
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Predicting accurate cathode properties of layered oxide materials using the SCAN meta-GGA density functional(使用SCAN meta-GGA密度泛函精确预测层状氧化物阴极材料的性质)
Arup ChakrabortyMudit DixitDoron Aurbach & Dan T. Major 
npj Computational Materials 4:60 (2018)
doi:s41524-018-0117-4
Published online:8 November 2018
Abstract| Full Text | PDF OPEN

摘要:层状锂嵌入过渡金属氧化物,是有望用于锂离子电池的阴极材料。本研究仔细梳理了最近开发的强约束和适当规范(SCAN)密度泛函方法,以此研究了原型阴极材料LiNiO2LiCoO2LiMnO2在不同锂嵌入极限下的结构、磁性和电化学性质。我们的研究表明,SCAN优于早期流行的泛函组合,在不使用Hubbard参数情况下,能得到与实验更为一致的结果,且受色散校正的影响很小。特别地,SCANPerdew-Burke-ErnzerhofPBE)泛函能更好地预测带隙和绝对电压,优于PBE + U预测电子态密度和电压分布,也优于PBEPBE + U预测电子密度和原位晶格常数。SCAN整体性能表现更好,可归因于局域态处理的改善和短程色散相互作用的更好描述   

Abstract:Layered lithium intercalating transition metal oxides are promising cathode materials for Li-ion batteries. Here, we scrutinize the recently developed strongly constrained and appropriately normed (SCAN) density functional method to study structural, magnetic, and electrochemical properties of prototype cathode materials LiNiO2, LiCoO2, and LiMnO2 at different Li-intercalation limits.We show that SCAN outperforms earlier popular functional combinations, providing results in considerably better agreement with experiment without the use of Hubbard parameters, and dispersion corrections are found to have a small effect.In particular, SCAN fares better than Perdew–Burke–Ernzerhof (PBE) functional for the prediction of band-gaps and absolute voltages, better than PBE+U for the electronic density of states and voltage profiles, and better than both PBE and PBE+U for electron densities and in operando lattice parameters.This overall better performance of SCAN may be ascribed to improved treatment of localized states and a better description of short-range dispersion interactions. 

Editorial Summary

Batteries: predicting cathodes(电池:预测阴极) 

各行各业对能源储存的需求不断增长。锂离子电池被视为满足这些需求的最有前途的技术选择之一。限制现代锂离子电池能量存储的关键因素,是阴极的电化学活性材料。现在来自以色列Bar-Ilan大学的Dan Major等,采用理论方法研究了三种原型层状阴极材料LiNiO2、LiCoO2和LiMnO2在不同Li嵌入极限下的结构细节、带隙、磁性、电子结构,以及形成能。所采用的强约束和适当规范泛函,提供了与大多数属性研究中的可用实验数据更为一致的结果,并证明强约束和适当规范泛函可作为精确预测材料性质的通用方法

There is an ever-growing demand for energy storage across a wide range of industries and markets. Lithium-ion batteries are viewed as one of the most promising technology choices to meet these needs.A key factor in limiting the amount of energy stored in modern lithium-ion batteries is the electrochemical active material in the cathode.Now, Dan Major and colleagues from Bar-Ilan University in Israel take a theoretical approach to investigate the structural details, band-gap, magnetic and electronic structure, and formation energy of three prototype layered cathode materials LiNiO2, LiCoO2, and LiMnO2at different Li-intercalation limits.The deployed strongly constrained and appropriately normed functional offers better agreement with available experimental data for most studied properties, and demonstrate itself to be a versatile method in materials computation for accurate property prediction.

Interplay between Kitaev interaction and single ion anisotropy in ferromagnetic CrI3 and CrGeTe3 monolayers (Kitaev相互作用与铁磁CrI3和CrGeTe3单层中的单离子各向异性的共同作用)
Changsong XuJunsheng FengHongjun Xiang & Laurent Bellaiche
npj Computational Materials 4:57 (2018)
doi:s41524-018-0115-6
Published online:5 November 2018
Abstract| Full Text | PDF OPEN

摘要:二维(2D)磁性在自然界中很少见,但却是自旋电子学必不可少的内容,也是前沿基础研究的重要方向。要维持2D磁性的稳定,其关键要素是磁各向异性。最近对CrI3和CrGeTe3单层膜的研究,不仅实现了人们一直在寻求的2D铁磁性,还揭示了两个系统中不同的磁各向异性,即CrI3的Ising行为与CrGeTe3的Heisenberg行为。这样的磁性差异与这两种材料的结构和电子相似性形成了强烈对比。若能在微观尺度上理解其机理,将对相关研究大有裨益。本研究采用第一原理计算和分析,给出了简单的哈密顿量,用以研究CrI3和CrGeTe3单层磁各向异性。令人吃惊的是,两个系统的交换相互作用被确定为Kitaev型。此外,我们发现,这种Kitaev相互作用和单离子各向异性(SIA)的共同作用,能够很自然地解释CrI3和CrGeTe3之间不同的磁性行为。最后,本研究进一步发现,Kitaev相互作用和SIA,都是通过重配体(CrI3的I或CrGeTe3的Te)自旋-轨道耦合而诱导的,而不是通常认为的通过3d磁性Cr离子而诱导的   

Abstract:Magnetic anisotropy is crucially important for the stabilization of two-dimensional (2D) magnetism, which is rare in nature but highly desirable in spintronics and for advancing fundamental knowledge.Recent works on CrI3 and CrGeTe3 monolayers not only led to observations of the long-time-sought 2D ferromagnetism, but also revealed distinct magnetic anisotropy in the two systems, namely Ising behavior for CrI3 versus Heisenberg behavior for CrGeTe3.Such magnetic difference strongly contrasts with structural and electronic similarities of these two materials, and understanding it at a microscopic scale should be of large benefits.Here, first-principles calculations are performed and analyzed to develop a simple Hamiltonian, to investigate magnetic anisotropy of CrI3 and CrGeTe3monolayers.The anisotropic exchange coupling in both systems is surprisingly determined to be of Kitaev-type.Moreover, the interplay between this Kitaev interaction and single ion anisotropy (SIA) is found to naturally explain the different magnetic behaviors of CrI3 and CrGeTe3.Finally, both the Kitaev interaction and SIA are further found to be induced by spin–orbit coupling of the heavy ligands (I of CrI3 or Te of CrGeTe3) rather than the commonly believed 3d magnetic Cr ionsviors. 

Editorial Summary

Monolayer magnetism: Kitaev interaction comes into play (单层磁性:Kitaev相互作用的结果) 

两种各向异性相互作用,即Kitaev相互作用和单离子型各向异性的共同作用是铁磁薄膜中具有磁性的原因。来自中国复旦大学的向红军教授和美国阿肯色大学的Laurent Bellaiche教授等,通过第一性原理计算,阐明了两种相似的二维铁磁材料表现出不同磁各向异性的机理。他们通过发展哈密顿量和紧束缚模型,揭示了铬-碘和铬-锗-碲两种单层中二维磁各向异性的起源,即Kitaev各向异性与单离子各向异性之间不同的共同作用方式。Kitaev和单离子各向异性都是由重配体元素碘和碲的自旋轨道耦合引起的。在非传统体系中研究Kitaev相互作用有助于更好地发现和理解有趣的物理现象

Interplay between two anisotropic interactions—Kitaev and single-ion—is responsible for magnetism in ferromagnetic thin films. Teams led by Hongjun Xiang at Fudan University in China and Laurent Bellaiche at the University of Arkansas in the US led to the use of first-principles calculations to elucidate magnetic anisotropy in two different two-dimensional ferromagnetic materials with different magnetic behaviors.By developing a predictive Hamiltonian and a tight-binding model, the origin of two-dimensional magnetism in chromium–iodine and chromium–germanium–tellurium monolayers was revealed to be Kitaev interactions and their interplay with single-ion anisotropy.Both the Kitaev and single-ion anisotropies were induced by the spin–orbit coupling of the heavy ligand elements iodine and tellurium. Research into Kitaev interactions in unconventional systems may contribute towards better understanding of interesting physics.

Nanoembryonicthermoelastic equilibrium and enhanced properties of defected pretransitional materials (含缺陷预转变材料:纳米胚胎热弹性平衡与性能增强)
Ye-Chuan XuWei-Feng RaoJohn W. Morris Jr. & Armen G. Khachaturyan
npj Computational Materials 4:58 (2018)
doi:s41524-018-0114-7
Published online:5 November 2018
Abstract| Full Text | PDF OPEN

摘要:位移型相变材料在相变温度以上经常可观察到异常的热学、力学和磁性行为。这些异常的材料性质通常是从电子/原子的本征响应的角度来解释。本文研究表明,在具有高密度缺陷的预转变材料中,这些性质也可以由非本征的热弹平衡效应产生。缺陷(位错或共格沉淀)附近的应力集中有可能在纳米尺寸的区域内发生应力诱导的相变,产生平衡态的纳米产物相胚胎。这些纳米胚胎处于一种热弹平衡状态,能够在外应力或者磁场的作用下无耗散地改变其平衡尺寸,从而使得材料具有超弹性和超磁致伸缩效应。降温过程中胚胎也有类似的响应,可以解释实验上观测的弥散相变和热膨胀系数以及有效弹性模量的改变,进而可解释受热不改变形状和弹性模量的因瓦和艾林瓦效应   

Abstract:Behaviors of displacive phase-transforming materials above the temperature of transformation, where abnormal thermal, elastic, magnetic properties are often observed, are mostly explained by intrinsic peculiarities in electronic/atomic structure. Here, we show these properties may also be attributed to extrinsic effects caused by a thermoelastic equilibrium in highly defected pretransitional materials.We demonstrate that the stress concentration near stress-generating defects such as dislocations and coherent precipitates could result in the stress-induced transformation within nanoscale regions, producing equilibrium embryos of the product phase.These nanoembryos in thermoelastic equilibrium could anhysteretically change their equilibrium size in response to changes in applied stress or magnetic fields leading to superelasticity or supermagnetostriction.Similar response to cooling may explain the observed diffuse phase transformation, changes in the coefficient of thermal expansion and effective elastic modulus, which, in turn, may explain the invar and elinvar behaviors. 

Editorial Summary

Displacive transformations: nano-embryos enhance properties(位移型相变:纳米胚胎增强材料性能) 

在金属的原子晶格中,缺陷产生的应力可导致纳米尺度区域的相变。南京信息工程大学的国家“千人计划”饶伟锋教授团队使用微弹性相场模拟研究了位移型相变材料中缺陷周围的局部应力场。研究发现,该应力场能够在相变温度以上促进稳定的纳米产物相胚胎的形成。纳米胚胎的尺寸由温度和晶格应变决定,其改变能增强材料对外应力或磁场改变的敏感性。纳米胚胎的这些行为有助于更好地理解橡胶金属中的超弹性效应、铁基形状记忆合金中的超磁致伸缩效应,以及受热不改变形状和弹性模量的因瓦和艾林瓦效应

Defects that generate stress in a metallic atomic lattice can lead to phase transformations in nanoscale regions. Research led by Wei-Feng Rao at the Nanjing University of Information Science and Technology in Chinaused phase field microelasticity simulations to examine local stress around defects (such as dislocations and nanoprecipitates) in materials that undergo displacive martensitic transformations at a certain temperature.They found that stress fields around defects promoted the formation of stable nano-embryos of the product phase even above the transformation temperature.The size of the nano-embryos depended on the strained lattice and temperature, enhancing their sensitivity to external changes in applied stress or magnetic field.The behavior of these nano-embryos can help better understand the superelastic effect in gum metals, supermagnetostriction in iron-based shape memory alloys, and the invar and elinvar effectscs.

Quantum effects on dislocation motion from ring-polymer molecular dynamics (量子效应对环-聚合物分子动力学中位错运动的影响)
Rodrigo FreitasMark Asta & Vasily V. Bulatov
npj Computational Materials 4:55 (2018)
doi:s41524-018-0112-9
Published online:22 October 2018
Abstract| Full Text | PDF OPEN

摘要:原子的量子运动也称为零点振动,最近被提出来用以解释铁和其它高原子质量金属中长期存在的理论计算和实验测量的低温塑性强度之间的误差。这一理论挑战了传统观念,即在重原子组成的固体中,原子的量子运动通常来说并不重要。本研究通过环-聚合物分子动力学(Ring-Polymer Molecular Dynamics,RPMD)对位错运动的量子效应作了量子动力学模拟。为了将量子原子模拟扩展到普适缺陷的相干长度和时间尺度上,我们在开源代码LAMMPS中实现了RPMD,从而使RPMD方法可广泛应用于该领域。我们使用RPMD/LAMMPS方法直接计算了位错迁移率及其对α-Fe屈服强度的影响。模拟结果表明,在温度低于50 K时,存在较为明显的量子效应,但也仅仅降低了大约13%的Peierls势垒。而相比于基于谐波过渡态理论的模拟结果,两套方法在Peierls相变势垒的降低程度上给出了截然不同的结果。本研究证实,零点振动为原子运动提供了充足的额外扰动,但其效果随着温度的升高而降低,即零点振动对位错迁移率的增强作用在很大程度上被升温后增加的有效原子尺寸所抵消,出现量子弥散效应,而这在以前的工作中一直都被忽略了   

Abstract:Quantum motion of atoms known as zero-point vibration was recently proposed to explain a long-standing discrepancy between theoretically computed and experimentally measured low-temperature plastic strength of iron and possibly other metals with high atomic masses. This finding challenges the traditional notion that quantum motion of atoms is relatively unimportant in solids comprised of heavy atoms.Here we report quantum dynamic simulations of quantum effects on dislocation motion within the exact formalism of Ring-Polymer Molecular Dynamics (RPMD).To extend the reach of quantum atomistic simulations to length and time scales relevant for extended defects in materials, we implemented RPMD in the open-source code LAMMPS thus making the RPMD method widely available to the community.We use our RPMD/LAMMPS approach for direct calculations of dislocation mobility and its effects on the yield strength of α-iron.Our simulation results establish that quantum effects are noticeable at temperatures below 50?K but account for only a modest (≈13% at T?=?0?K) overall reduction in the Peierls barrier, at variance with the factor of two reduction predicted earlier based on the more approximate framework of harmonic transition state theory.Our results confirm that zero-point vibrations provide ample additional agitation for atomic motion that increases with decreasing temperature, however its enhancing effect on dislocation mobility is largely offset by an increase in the effective atom size, an effect known as quantum dispersion that has not been accounted for in the previous calculations. 

Editorial Summary

Dislocations: ring-polymer molecular dynamics incorporates quantum effects(位错:环-聚合物分子动力学包含量子效应) 

环-聚合物大分子动力学可以准确地模拟量子效应对位错运动的影响。来自美国加州大学伯克利分校和劳伦斯利弗莫尔国家实验室的Rodrigo Freitas领导的研究小组,研究了原子的量子运动对Peirels应力的影响,即材料的耐低温位错运动。与实验相比,经典分子动力学对Peirels应力有所高估,但通过并行计算对150000个原子进行环-聚合物分子动力学模拟与实验值差异较小。这表明,早期的量子修正高估了零点振动对体系的扰动,同时低估了近邻原子的约束效应。采用有效的环-聚合物分子动力学模拟可以帮助我们研究材料中普适的缺陷,同时可以准确地计算原子动力学的量子修正

Large ring-polymer molecular dynamics can accurately simulate quantum effects on dislocation motion. A team led by Rodrigo Freitas at the University of California, Berkeley and Lawrence Livermore National Laboratory, U.S.A., investigated the effect of atomic quantum motion on the Peirels stress, i.e., the low-temperature resistance to dislocation motion. While classical molecular dynamics yielded the expected overestimation of the Peirels stress compared to experiments, ring-polymer molecular dynamics on 150,000 atoms using parallel computing showed a smaller discrepancy between simulations and experiments.This indicated that earlier quantum corrections overestimated the agitation effect of zero-point-vibrations and downplayed the effect of atomic neighbor confinement.Implementing efficient ring-polymer molecular dynamics can help us study extended defects in materials, while accurately accounting for quantum corrections to atom dynamics.

Design of 2D massless Dirac fermion systems and quantum spin Hall insulators based on sp–sp2 carbon sheets (基于sp-sp2碳层状材料设计2D无质量Dirac费米子系统和量子自旋霍尔绝缘子)
Minwoo ParkYoungkuk Kim & Hoonkyung Lee
npj Computational Materials 4:54 (2018)
doi:s41524-018-0113-8
Published online:18 October 2018
Abstract| Full Text | PDF OPEN

摘要:石墨烯是一种无质量的狄拉克费米子系统,在动量空间中具有狄拉克点。石墨烯因具有自旋轨道耦合(SOC),也首次被确定为量子自旋霍尔(QSH)绝缘体,它能在狄拉克点处打开带隙。这一发现为研究QSH效应及其在量子计算和自旋电子学方面的应用打开了新方向。虽然在HgTe量子阱中已经观测到了QSH效应,但是由于石墨烯的SOC强度太小(~1μeV),无法在实验可实现的温度范围内诱导出拓扑绝缘体相。为此,我们设计了二维sp-sp2杂化碳层,并进行了系统的原子模拟,以发现新的具有QSH相的狄拉克系统。我们从31个新发现的碳层中确定了21个碳层是狄拉克费米子系统,但不具备SOC,与石墨烯在布里渊区内出现的狄拉克锥的数量、形状和位置都大相径庭。此外,我们发现,在21个新的狄拉克费米子系统中,有19个可以成为QSH绝缘体,其具有相当大的SOC带隙,达到meV级,从而在实验可达温度下实现QSH效应。此外,基于26个狄拉克费米子系统,我们将无SOC情况下狄拉克点的数目与有SOC情况下的QSH相建立了联系。本研究为具有理想性能的拓扑材料的设计提供了新的前景   

Abstract:Grapheneis a massless Dirac fermion system, featuring Dirac points in momentum space.It was also first identified as a quantum spin Hall (QSH) insulator when considering spin–orbit coupling (SOC), which opens a band gap at the Dirac points.This discovery has initiated new research efforts to study the QSH effect, towards its application for quantum computing and spintronics.Although the QSH effect has been observed in HgTe quantum wells, the SOC strength of graphene is too small (~1?μeV) to induce the topological insulator phase in an experimentally achievable temperature regime.Here, we perform a systematic atomistic simulation to design two-dimensional sp–sp2hybrid carbon sheets to discover new Dirac systems, hosting the QSH phase.21 out of 31 newly discovered carbon sheets are identified as Dirac fermion systems without SOC, distinct from graphene in the number, shape, and position of the Dirac cones occurring in the Brillouin zone.Moreover, we find 19 out of the 21 new Dirac fermion systems become QSH insulators with a sizable SOC gap enhanced up to an order of meV, thus allowing for the QSH effect at experimentally accessible temperatures.In addition, based on the 26 Dirac fermion systems, we make a connection between the number of Dirac points without SOC and the resultant QSH phase in the presence of SOC.Our findings present new prospects for the design of topological materials with desired properties. 

Editorial Summary

Atomistic simulations: design of two-dimensional carbon-based Dirac materials (原子模拟:2D碳基Dirac材料的设计) 

利用第一性原理可以预测各种无质量狄拉克锥的碳基系统。来自韩国建国大学的Hoonkyung Lee领导的研究小组利用原子模拟进行了系统的结构搜索和几何优化,以探索和设计能够容纳量子自旋霍尔相的原子级层状碳材料(2D材料)。从二维sp2-sp2杂化网络开始,原子模拟提供了31个碳层,这些碳层都具有各种类型无质量的狄拉克锥,同时包括各向同性或各向异性的狄拉克锥,以及共存的具有不同各向异性的不对称狄拉克锥。此外,他们还发现了21个没有自旋轨道耦合的狄拉克费米子系统,其中的19个有可能成为量子自旋霍尔绝缘体,却具有相当大的自旋轨道耦合。这些结果为揭示二维材料中实现狄拉克锥提供了可行路线

A variety of carbon-based systems with massless Dirac cones can be predicted by first principles. A team led by Hoonkyung Lee at Konkuk University performed a systematic structure search and geometry optimization using atomistic simulations, to explore and design atomically thin carbon materials capable of hosting a quantum spin Hall phase.Starting from two-dimensional sp2–sp2 hybrid networks, the atomistic simulations provided thirty-one carbon sheets featuring various types of massless Dirac-cone systems, including isotropic or anisotropic Dirac cones, and coexisting asymmetric Dirac cones with different anisotropic directions.Furthermore, twenty-one systems were found to host Dirac fermions without spin-orbit coupling, and nineteen of these may become quantum spin Hall insulators with a sizeable spin-orbit coupling.These results highlight a feasible route towards Dirac cone engineering in two-dimensional materials.

Mechanism of contact pressure-induced friction at the amorphous carbon/alpha olefin interface (无定形碳/α烯烃界面处因接触压力引起的摩擦机理)
Xiaowei LiAiying Wang & Kwang-Ryeol Lee
npj Computational Materials 4:53 (2018)
doi:s41524-018-0111-x
Published online:26 September 2018
Abstract| Full Text | PDF OPEN

摘要:将无定形碳(a-C)膜与润滑油组合可以显着改善移动机械部件的摩擦性能和寿命。然而,暴露于高接触压力时,由于缺乏界面结构的有关信息,因此不能很好地了解摩擦机理。本研究选择线性α-烯烃(C5H10)作为润滑剂,并通过反应分子动力学模拟,研究接触压力下a-C / C5H10 / a-C滑动界面结构的演变。我们的结果表明,与无润滑剂相比,将C5H10引入a-C / a-C界面可使摩擦系数降低多达93%,尽管润滑效率很大程度上取决于接触压力。特别地,增加接触压力不仅引起润滑剂与α-C的结合,还促进C5H10碳-碳骨架经特定的断裂而解离,这决定了摩擦行为。本研究结果揭示了潜在的润滑机理,并据此可开发新型长寿命有效润滑系统   

Abstract:Combining an amorphous carbon (a-C) film with a lubricating oil can significantly improve the friction performance and lifetime of moving mechanical components. However, the friction mechanism is not well understood owing to a lack of information regarding the structure of the interface when exposed to high contact pressure.Here, we select linear alpha olefin, C5H10, as a lubricant and study the evolution of the structure of the a-C/C5H10/a-C sliding interface under contact pressure via reactive molecular dynamics simulation.Our results suggest that introducing C5H10 into the a-C/a-C interface reduces the friction coefficient by up to 93% compared with no lubricant, although the lubricating efficiency strongly depends on the contact pressure.In particular, increasing the contact pressure not only induces the binding of the lubricant with a-C, but also facilitates the dissociation of the C5H10 carbon-carbon skeleton by specific scissions, which governs the friction behavior.These results disclose the underlying lubrication mechanism and could enable the development of new and effective lubricating systems with long lifetimes. 

Editorial Summary

Friction: pressure key to lubrication (摩擦:把重点对准润滑机理) 

将无定形碳膜与润滑油结合虽可改善摩擦性能,但它还是取决于接触压力。来自韩国科学技术研究院的Xiaowei Li和Kwang-Ryeol Lee领导的团队,利用分子动力学模拟研究了两种无定形碳膜与润滑剂烯烃油之间的摩擦。令人惊讶的是,在两个表面在滑动期间,增加压力会导致摩擦减小,接触压力继续增大,摩擦又会增加。这是由于压力增加使油分子分离,其中的碎片重新与无定形碳表面组合,使它们钝化。然而,在高压下表面的钝化在降低摩擦方面,不如在中等压力下油流体动力润滑那样有效。了解压力和油在摩擦中的作用可以帮助指导我们改进润滑剂的设计

While combining an amorphous carbon film with lubricating oil can improve friction performance, it depends on contact pressure. A team led by Xiaowei Li and Kwang-Ryeol Lee from the Korea Institute of Science and Technology used molecular dynamics simulations to investigate the friction of two amorphous carbon films with olefin oil as lubricant.Surprisingly, increasing pressure during sliding caused a decrease followed by an increase in the friction between the two surfaces. This was due to increasing pressure dissociating the oil molecules, fragments of which recombined with the amorphous carbon surfaces to passivate them.Passivation of the surfaces at high pressures, however, was not as efficient at reducing friction as hydrodynamic lubrication from the oil at medium pressures.Understanding the role of pressure and oils in friction can help guide our design of improved lubricants.

Materials structure genealogy and high-throughput topological classification of surfaces and 2D materials (表面和2D材料的结构谱系及高通量拓扑分类)
Lauri HimanenPatrick Rinke & Adam Stuart Foster
npj Computational Materials 4:52 (2018)
doi:s41524-018-0107-6
Published online:11 September 2018
Abstract| Full Text | PDF OPEN

摘要:为了处理存储在各种计算材料数据库中的大量信息,对原子结构作自动化和可验证的结构分类,正变得必不可少。本研究提出了对原子系统作结构分类的一般递归方案,介绍了结构材料图,用以整理材料结构系谱。还介绍了如何实施2D结构的自动分类,尤其是表面和2D材料的自动分类。分类程序能自动确定结构的维数,将结构分为表面或2D材料,再恢复基础单元晶胞,最后识别诸如吸附物等离群原子。该分类方案不需要明确的搜索模式,即使结构存在缺陷和位错也能工作。对各种原子结构所作的测试结果显示,其能为所有恢复结构特性提供高精度测定。分类算法的软件只要使用开源许可证便可免费获得安装启用   

Abstract:Automated and verifiable structural classification for atomistic structures is becoming necessary to cope with the vast amount of information stored in various computational materials databases.Here we present a general recursive scheme for the structural classification of atomistic systems and introduce a structural materials map that can be used to organize the materials structure genealogy.We also introduce our implementation for the automatic classification of two-dimensional structures, especially focusing on surfaces and 2D materials.This classification procedure can automatically determine the dimensionality of a structure, further categorize the structure as a surface or a 2D material, return the underlying unit cell and also identify the outlier atoms, such as adsorbates.The classification scheme does not require explicit search patterns and works even in the presence of defects and dislocations.The classification is tested on a wide variety of atomistic structures and provides a high-accuracy determination for all of the returned structural properties.A software implementation of the classification algorithm is freely available with an open-source license. 

Editorial Summary

Classification algorithm: high-throughput automatic screening of surfaces and 2D materials(分类算法:表面和2D材料的高通量自动筛选) 

该研究报道了一种分类算法,可以自动分类表面和2D材料的原子结构。来自芬兰阿尔托大学的一个研究小组,开发了一种通用的递归计算方案,用于根据系谱进行结构和原子系统的整理分类。该工具以NOMAD存档作为基准,用来在含有异构数据的实际数据库环境中测试分类的准确性。这种拓扑分类方法能够检测基础单元晶胞和离群原子,例如表面和2D材料上的吸附物。软件功能的执行可以集成在提供原子几何图形的现有数据库上,使用开源许可证

A classification algorithm can automatically categorize the atomic structure of surfaces and 2D materials. A research team at Aalto University has developed a general recursive computational scheme for the classification of structures and atomistic systems that are organized based on their genealogy.The tool uses the NOMAD archive as benchmark for testing the classification accuracy in a realistic database environment containing heterogeneous data.This topological classification approach is capable of detecting the underlying unit cell and outlier atoms such as adsorbates in surfaces and 2D materials.The software implementation can be integrated on existing databases that provide atomistic geometries and is available with an open-source license.

Efficient search of compositional space for hybrid organic–inorganic perovskites via Bayesian optimization (通过贝叶斯优化有效搜索杂化有机-无机钙钛矿的成分空间)
Henry C. HerbolWeici HuPeter FrazierPaulette Clancy & Matthias Poloczek
npj Computational Materials 4:51 (2018)
doi:s41524-018-0106-7
Published online:10 September 2018
Abstract| Full Text | PDF OPEN

摘要:在新材料发现过程中,人们对通过机器学习技术实现快速搜索的兴趣,越来越浓。一个典型的例子就是,最终形成太阳能电池薄膜材料——被称为有机-无机杂化钙钛矿(HOIP)——的溶液组分如何选配。在溶液中结合形成这些薄膜的分子种类,其数量构成了极大的“组合”空间(有时,超过500,000种可能的组合)。选择具有所需特性的HOIP涉及从多种可选的原料中选择不同的阳离子、卤化物和溶剂混合物。通过实验研究或分子模拟进行的无理论指导的搜索会非常昂贵。本研究提出了一种贝叶斯优化方法,即采用特种应用程序的内核来克服数据稀缺的困难,其中的搜索空间由指示某种成分是否存在的二进制变量给出。我们证明了本方法能以HOIP盐与溶剂之间的最大分子间结合能来确定HOIPs目标分子,其确定成本比先前最先进的贝叶斯优化法低得多,而且完成详尽搜索所需的时间短得多(不到原来的10%)。在包含72种组合的HOIP组成空间中,我们找到最佳组成的迭代次数不超过15±10次,并且在涉及混合卤化物(240种组合)时,迭代次数不超过31±9次。我们用所有可能组合的穷举量子力学模拟验证了贝叶斯优化方法的最优预测。本研究证明,所报道的贝叶斯优化法有望应用于新材料发现   

Abstract:Accelerated searches, made possible by machine learning techniques, are of growing interest in materials discovery. A suitable case involves the solution processing of components that ultimately form thin films of solar cell materials known as hybrid organic–inorganic perovskites (HOIPs).The number of molecular species that combine in solution to form these films constitutes an overwhelmingly large “compositional” space (at times, exceeding 500,000 possible combinations).Selecting a HOIP with desirable characteristics involves choosing different cations, halides, and solvent blends from a diverse palette of options.An unguided search by experimental investigations or molecular simulations is prohibitively expensive.In this work, we propose a Bayesian optimization method that uses an application-specific kernel to overcome challenges where data is scarce, and in which the search space is given by binary variables indicating whether a constituent is present or not.We demonstrate that the proposed approach identifies HOIPs with the targeted maximum intermolecular binding energy between HOIP salt and solvent at considerably lower cost than previous state-of-the-art Bayesian optimization methodology and at a fraction of the time (less than 10%) needed to complete an exhaustive search.We find an optimal composition within 15?±?10 iterations in a HOIP compositional space containing 72 combinations, and within 31?±?9 iterations when considering mixed halides (240 combinations).Exhaustive quantum mechanical simulations of all possible combinations were used to validate the optimal prediction from a Bayesian optimization approach.This paper demonstrates the potential of the Bayesian optimization methodology reported here for new materials discovery. 

Editorial Summary

Bayesian optimization: accelerated perovskites and solvent screening (贝叶斯优化:加速钙钛矿和溶剂的筛选) 

该研究开发了一种更便宜、更有效的优化方法用以筛选有机-无机钙钛矿中的组成与溶剂的相互作用。由美国亚利桑那大学的Matthias Poloczek领导的一个合作小组提出了一种改进的贝叶斯优化法,用于预测各种杂化有机-无机钙钛矿和溶剂的最佳组合。他们筛选了240种可能的钙钛矿-溶剂组合的分子间结合能,发现FAPbI2Cl和四氢噻吩1-氧化物的分子间结合能最大。与先前最先进的贝叶斯优化方法相比,采用特种应用程序的内核来克服数据稀缺之类的困难,显着降低了计算成本。作者所报道的改进方法,可扩展应用于对混合离子和混合卤化物/阳离子系统的筛选,也可应用于解决广泛材料的设计和优化问题

A cheaper and more effective optimization method has been developed to screen composition and solvent interactions in organic–inorganic perovskites. A collaborative team led by Matthias Poloczek from University of Arizona, USA, propose a modified Bayesian optimization method to predict the optimal combination of various hybrid organic–inorganic perovskites and solvents.They screen the intermolecular binding energy of 240 possible perovskite-solvent combinations, finding that the maximum occurs for FAPbI2Cl and tetrahydrothiophene 1-oxide.The use of an application-specific kernel overcomes challenges such as data scarcity and reduces the computational cost substantially compared to previous state-of-the-art Bayesian optimization methods.The described method can be extended to study mixed ions and mixed halide/cation systems, and could be applicable to a wide range of materials design and optimization problems.

Microstructure design using graphs(基于图形的微结构设计)
Pengfei DuAdrian ZebrowskiJaroslaw ZolaBaskar Ganapathysubramanian & Olga Wodo
npj Computational Materials 4:50 (2018)
doi:s41524-018-0108-5
Published online:7 September 2018
Abstract| Full Text | PDF OPEN

摘要:具有定制微结构的薄膜是一类新兴材料,其应用包括电池电极、有机电子器件和生物传感器。这种薄膜器件通常具有受限的多相微结构,并且有很强的各向异性。目前的微结构设计方法集中在体性质的优化,即对代表性块体上统计平均的特征进行调整优化。本研究报告了一种用于形态发生的工具,该工具是基于图形的优化问题,演化了识别约束和各向异性约束的微结构。我们通过面向光伏应用的优化形态设计介绍了该方法,将初始形态演变为优化形态,展示出显著改善的短路电流(与传统的体异质结形态相比改善了68%)。我们展示了一系列厚度的优化形态,表现出自相似行为。研究结果提示,厚一些的薄膜(250nm)可用于收集更多的入射光能量。该基于图形的形态发生(微结构设计),可广泛适用于微结构起重要作用的电池、生物传感器等相关领域   

Abstract:Thin films with tailored microstructures are an emerging class of materials with applications such as battery electrodes, organic electronics, and biosensors. Such thin film devices typically exhibit a multi-phase microstructure that is confined, and show large anisotropy. Current approaches to microstructure design focus on optimizing bulk properties, by tuning features that are statistically averaged over a representative volume.Here, we report a tool for morphogenesis posed as a graph-based optimization problem that evolves microstructures recognizing confinement and anisotropy constraints.We illustrate the approach by designing optimized morphologies for photovoltaic applications, and evolve an initial morphology into an optimized morphology exhibiting substantially improved short circuit current (68% improvement over a conventional bulk-heterojunction morphology).We show optimized morphologies across a range of thicknesses exhibiting self-similar behavior.Results suggest that thicker films (250?nm) can be used to harvest more incident energy.Our graph based morphogenesis is broadly applicable to microstructure-sensitive design of batteries, biosensors and related applications. 

Editorial Summary

MATERIALS DESIGN: The power of graphs (材料设计:图形的威力) 

以图形表示微结构,并以数学方式映射它们的属性,可以帮助改进材料属性。形态发生(微结构设计)是优化器件性能的过程;用适当的数学框架表示候选结构以探测它们的属性,再将结构映射到属性。就这两个步骤来说,目前的方法计算量很大,但现在美国爱荷华州立大学和布法罗大学的研究团队,用标记的、加权的、无向图来表示结构,简化了该优化过程。在此基础上,可以通过通用物理图形描述符(如路径长度、域的大小)和某个感兴趣属性的加权函数来创建“替代”模型。这种方法虽然只作为改进有机太阳能电池的新设计方法,但也可以扩展应用于其他领域

Representing microstructures with graphs, and mapping their properties mathematically, can help improve material properties.Morphogenesis is the process of optimizing performance in devices; representing the candidate structure with an appropriate mathematical framework in order to probe their properties and then mapping the structure to a property.Current approaches rely on computationally heavy methods for both stages, but now a team from Iowa State University and University at Buffalo simplify the process by representing the structures with labelled, weighted, undirected graphs.On this basis, one can create a “surrogate” model through generic physics graph descriptors (e.g. path lengths, domain sizes) and weighting functions for the particular property of interest.This approach reveals new designs for improved organic solar cells, but could expanded to other devices.

Online search tool for graphical patterns in electronic band structures (电子能带结构图形图案的在线搜索工具)
Stanislav S. BorysovBart OlsthoornM. Berk GedikR. Matthias Geilhufe & Alexander V. Balatsky
npj Computational Materials 4:46 (2018)
doi:s41524-018-0104-9
Published online:20 August 2018
Abstract| Full Text | PDF OPEN

摘要:许多功能材料以其电子能带结构具有的特定模式为特征,例如,Dirac材料以能带的线性交叉为特征,拓扑绝缘体以“墨西哥帽”图案为特征,有效自由电子气以抛物线分散为特征。为了成功找到这些材料的电子能带特征图形图案,手动检查少量材料的电子能带结构还是比较容易的。然而现代电子能带结构数据库中的数据量不断增加,手动查找已不切实际。为了解决这个问题,本研究开发了一种图形图案的自动搜索工具,用来在有机材料数据库(Organic Materials Database)的电子能带结构中搜索。该工具能够通过在线高通量计算,于数千个能带结构集合中,找到用户指定的图形图案。使用这一工具,只需几秒钟即可为26,739个有机晶体在费米面附近的10个电子能带内找到任意图形图案。开发工具适用于任何其他电子能带的结构数据库,而且免费提供源代码   

Abstract:Many functional materials can be characterized by a specific pattern in their electronic band structure, for example, Dirac materials, characterized by a linear crossing of bands; topological insulators, characterized by a “Mexican hat” pattern or an effectively free electron gas, characterized by a parabolic dispersion.To find material realizations of these features, manual inspection of electronic band structures represents a relatively easy task for a small number of materials. However, the growing amount of data contained within modern electronic band structure databases makes this approach impracticable. To address this problem, we present an automatic graphical pattern search tool implemented for the electronic band structures contained within the Organic Materials Database. The tool is capable of finding user-specified graphical patterns in the collection of thousands of band structures from high-throughput calculations in the online regime. Using this tool, it only takes a few seconds to find an arbitrary graphical pattern within the ten electronic bands near the Fermi level for 26,739 organic crystals. The source code of the developed tool is freely available and can be adapted to any other electronic band structure database. 

Editorial Summary

New materials: online searching (新材料:在线搜索) 

该研究开发了一种依据电子能带结构中所选图形图案,从数据库中寻找候选材料的在线搜索工具。瑞典Nordita、KTH皇家理工学院和斯德哥尔摩大学的Alexander V. Balatsky教授的团队提供了一个在线搜索工具,用于查找有机材料数据库中包含的电子能带结构数据中的某些图形图案。该工具能在几秒钟内从数据库数千个带结构的集合内、费米面附近的十个电子能带中,找到任意给定的图形图案。电子能带结构的图形图案可作为Dirac材料、拓扑绝缘体、自由电子气等的特征。该工具可对无法手动检查的大量带结构进行自动在线分析

An online search tool is developed to look for candidate materials by exploring chosen graphical patterns in their electronic band structure from a database.A team led by Alexander V. Balatsky from Nordita, KTH Royal Institute of Technology and Stockholm University present an online search tool to find certain graphical patterns in the electronic band structure data contained within the Organic Materials Database.The tool is capable of finding an arbitrary graphical pattern within the ten electronic bands near the Fermi level in the collection of thousands of band structures in the database within a few seconds.The graphical patterns can be features of Dirac materials, topological insulators, free electron gas, etc. This tool allows for an automatic online analysis for a large collection of band structures where manual inspection is impractical.

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