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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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In silico designing of power conversion efficient organic lead dyes for solar cells using todays innovative approaches to assure renewable energy for future (太阳能电池中高转换效率有机铅染料:基于当前计算模拟的创新设计、确保未来的可再生能源) 
Supratik KarJuganta K. Roy & Jerzy Leszczynski
npj Computational Materials 3, Article number: 21 (2017)
doi:10.1038/s41524-017-0023-1
Published online:24 May 2017
Abstract| Full Text | PDF OPEN

摘要: 设计新型有机染料敏化剂并用于高转换效率的染料敏化太阳能电池可推动太阳能电池技术的进步,以避开硅基太阳能电池的诸多缺点。计算模拟研究包括定量构-性关系分析及量子化学分析可洞察碘电解质(11个不同化学族群中273个芳基胺有机染料)的主要电子转移机理和光物理特性。直接定量构-性关系模型能够识别化学分子的基本电子属性和结构属性,为11类芳胺有机染料分子性能的量化提供必要的前提条件,是筛选出染料敏化太阳能电池的高转换效率染料分子的基础。探索采用四氢喹啉,NN'-二烷基苯胺和二氢吲哚作为芳基胺有机染料用于染料敏化太阳能电池的研究却鲜见报道。因此,本研究在铅染料设计中采用了上述类别的相应定量构-性关系模型对染料性质进行计算识别。然后对设计的染料的一系列电化学和光物理参数作了计算预测,以确定染料敏化太阳能电池中所需要的电子流动参量。最终通过组合计算技术给出了7种有前途的铅染料,分别用于所考察的所有三类分子(四氢喹啉,NN'-二烷基苯胺和二氢吲哚)。与现有染料的最高实验转换效率相比,这三类染料的最高预测转换效率值(%,experimental %power conversion efficiency value)分别增加了130%183%46%,可满足所需的电化学参数。   

Abstract: Advances in solar cell technology require designing of new organic dye sensitizers for dye-sensitized solar cells with high power conversion efficiency to circumvent the disadvantages of silicon-based solar cells. In silico studies including quantitative structure-property relationship analysis combined with quantum chemical analysis were employed to understand the primary electron transfer mechanism and photo-physical properties of 273 arylamine organic dyes from 11 diverse chemical families explicit to iodine electrolyte. The direct quantitative structure-property relationship models enable identification of the essential electronic and structural attributes necessary for quantifying the molecular prerequisites of 11 classes of arylamine organic dyes, responsible for high power conversion efficiency of dye-sensitized solar cells. Tetrahydroquinoline, N,N′-dialkylaniline and indoline have been least explored classes under arylamine organic dyes for dye-sensitized solar cells. Therefore, the identified properties from the corresponding quantitative structure-property relationship models of the mentioned classes were employed in designing of “lead dyes”. Followed by, a series of electrochemical and photo-physical parameters were computed for designed dyes to check the required variables for electron flow of dye-sensitized solar cells. The combined computational techniques yielded seven promising lead dyes each for all three chemical classes considered. Significant (130, 183, and 46%) increment in predicted %power conversion efficiency was observed comparing with the existing dye with highest experimental %power conversion efficiency value for tetrahydroquinoline, N,N′-dialkylaniline and indoline, respectively maintaining required electrochemical parameters. 

Editorial Summary

Photovoltaics: computers help design efficient solar cells (光伏电池:电脑帮助设计高效的太阳能电池) 

本研究定量设计了21种有望用于太阳能电池的染料,避免了冗长的帅选实验研究。来自西班牙杰克逊州立大学的Jerzy Leszczynski及其团队研究了11个化学分子家族中的数百种有机染料,将计算结果与实验数据相比较,确定了能提高太阳能电池效率的最重要的分子特性。以这些重要的分子特性作为准则,可设计一系列新型染料。其光学和电化学性质的计算模拟可使筛选的范围缩小。最后,他们预测了这些分子在染料敏化太阳能电池中的性能。采用组合计算技术他们确定了二十多种有前景的染料,能让实验科学家更快地合成和测试用所组装的太阳能电池。该方法还有助于设计更多其他化学家族中的分子用作太阳能电池染料。 

Twenty-one promising dyes for solar cells are designed numerically, avoiding lengthy screening experiments. A team led by Jerzy Leszczynski at the Jackson State University studied a collection of hundreds of organic dyes, in eleven chemical families, compared computational results to experimental data, and identified the most important molecular properties that lead to high solar cell efficiency. Using these important molecular properties as guidelines, a series of new dyes were designed. Simulations of their optical and electrochemical properties allowed narrowing down the selection. Finally, their performance in dye-sensitized solar cells was predicted. Using combined computational techniques, the researchers identified two dozen promising dyes for experimentalists to synthesize and to test solar cells more rapidly. The methodology may help design more molecules in other chemical families. 

Continuum understanding of twin formation near grain boundaries of FCC metals with low stacking fault energy (在连续介质尺度上揭示低堆垛层错能量的FCC金属晶界处孪晶形成机制)
Jaimyun JungJae Ik YoonJung Gi KimMarat I. LatypovJin You Kim & Hyoung Seop Kim
npj Computational Materials 3, Article number: 21 (2017)
doi:10.1038/s41524-017-0023-1
Published online:24 May 2017
Abstract| Full Text | PDF OPEN

摘要:低堆垛层错能量的面心立方金属晶界处,常可观察到变形孪晶发生deformation twinning。孪晶发生于晶界处的一个可能的促进因素是变形时的晶粒间相互作用。但这种相互作用对孪晶演化有何影响,人们却不太清楚。同时,微结构特征与孪晶形成之间的因果关系尽管已做了大量实验和模拟研究,却仍缺乏对大量晶粒聚集体之间清晰关系的理解。本研究通过室温下单轴拉伸变形的孪晶诱导可塑钢全场晶体可塑性模拟,探查了晶界附近的形变孪晶,从而表征了晶粒间相互作用的微观力学行为。首先通过电子反散射衍射技术观察了微结构,获得数据后,再经微结构合成建造技术(synthetic microstructure building),重建了统计学上等效的微结构。通过分析晶粒间微观力学响应,来研究拉伸变形条件下微结构大量要素在总体上的孪晶发生行为。模拟结果分析表明,晶粒相互作用可通过晶边处的应力转移或晶界附近的应力局域化,来改变晶界附近的局部力学行为。 

Abstract: Deformation twinning from grain boundaries is often observed in face-centered cubic metals with low stacking fault energy. One of the possible factors that contribute to twinning origination from grain boundaries is the intergranular interactions during deformation. Nonetheless, the influence of mechanical interaction among grains on twin evolution has not been fully understood. In spite of extensive experimental and modeling efforts on correlating microstructural features with their twinning behavior, a clear relation among the large aggregate of grains is still lacking. In this work, we characterize the micromechanics of grain-to-grain interactions that contribute to twin evolution by investigating the mechanical twins near grain boundaries using a full-field crystal plasticity simulation of a twinning-induced plasticity steel deformed in uniaxial tension at room temperature. Microstructures are first observed through electron backscatter diffraction technique to obtain data to reconstruct a statistically equivalent microstructure through synthetic microstructure building. Grain-to-grain micromechanical response is analyzed to assess the collective twinning behavior of the microstructural volume element under tensile deformation. Examination of the simulated results reveal that grain interactions are capable of changing the local mechanical behavior near grain boundaries by transferring strain across grain boundary or localizing strain near grain boundary. 

Editorial Summary(自然研究宣传稿)

Metals: grain neighbours influence twin formation during deformation(金属:相邻晶粒的相互作用影响变形过程中的孪晶形成)

不利于孪晶形成的晶粒却由于周围的晶粒相互作用显示出对孪晶形成的促进作用。来自韩国浦项科技大学的金贤勋及其同事,基于变形钢的位错滑移和孪生机制,对由各种取向晶粒合成而来的金属微观结构中变形行为进行模拟。孪晶首先起始于晶粒边界附近并依赖初始晶粒的取向,但随着进一步的变形,晶界一侧强大的孪晶活性,又在该晶界的另一侧引发了强烈的孪晶活性。甚至当边界另一边的晶粒不利于孪晶发生的时候,孪晶也照样能够发生。因此,研究相邻晶粒间的邻接关系很可能有助于优化由孪晶形成的合金。

Grains that should not favour twin formation exhibit twinning as a result of surrounding grains acting on their boundaries. A team led by HyoungSeop Kim at the Pohang University of Science and Technology in the Republic of Korea simulated the deformation of synthetic metallic microstructures with many grains of different orientations, based on steels that deform by both dislocation slip and twinning mechanisms. Twinning first started near grain boundaries and depended on initial grain orientation but, with further deformation, strong twin activity on one side of a boundary triggered strong twin activity on the other side of that boundary. This happened even when the grain on the other side of the boundary was unfavourable to twinning. Taking into account grain neighbourhood may therefore help in optimising twin-forming alloys.

 

Thermodynamic potential and phase diagram for multiferroic bismuth ferrite (BiFeO3) (多铁铋铁氧体(BiFeO3)的热力学势和相图) 
Dmitry V. Karpinsky, Eugene A. Eliseev, Fei Xue, Maxim V. Silibin, Alexandra Franz, Maya D. Glinchuk, Igor O. Troyanchuk, Sergey A. Gavrilov, Venkatraman Gopalan, Long-Qing Chen & Anna N. Morozovska
npj Computational Materials 3, Article number: 19 (2017)
doi:10.1038/s41524-017-0022-2
Published online:10 May 2017
Abstract| Full Text | PDF OPEN

摘要: 本研究构造了纯相和轻微掺杂的铁酸铋的Landau-Ginzburg热力学势与对应相图,铁酸铋在室温下是一种铁电反铁磁体。基于新的X射线和中子衍射实验发展的铁酸铋热力学势补充了目前已有的数据库。本研究证明了一个强大的四阶反铁磁畸变-类型偶(biquadratic antiferrodistortive-type coupling)和作用对定量描述Bi1-xLaxFeO3多铁相图,以及反铁磁、铁电和反铁磁畸变相的温度稳定性至关重要,其也可用来预测新颖中间结构相变。此外,我们的研究显示旋转磁性的反铁磁畸变-反铁磁耦合是描述BiFeO3R3c相的铁电极化和反铁磁畸变行为的非常重要方法。Landau-Ginzburg热力学势可描述连续和诱发型相变的序列、序参数的温度相关性、以及对外部刺激的相应敏感度。Landau-Ginzburg热力学势若与形状、尺寸和制备方法相关的表面能与能量梯度两个参量结合,则还可以用来预测Bi1-xLaxFeO3薄膜和纳米颗粒的相应铁电和反铁磁畸变性能。

Abstract: We construct a Landau–Ginzburg thermodynamic potential, and the corresponding phase diagram for pristine and slightly doped bismuth ferrite, a ferroelectric antiferromagnet at room temperature. The potential is developed based on new X-ray and neutron diffraction experiments complementing available data. We demonstrate that a strong biquadratic antiferrodistortive-type coupling is the key to a quantitative description of Bi1−x La x FeO3 multiferroic phase diagram including the temperature stability of the antiferromagnetic, ferroelectric, and antiferrodistortive phases, as well as for the prediction of novel intermediate structural phases. Furthermore, we show that “rotomagnetic” antiferrodistortive–antiferromagnetic coupling is very important to describe the ferroelectric polarization and antiferrodistortive tilt behavior in the R3c phase of BiFeO3. The Landau–Ginzburg thermodynamic potential is able to describe the sequence of serial and trigger-type phase transitions, the temperature-dependent behavior of the order parameters, and the corresponding susceptibilities to external stimuli. It can also be employed to predict the corresponding ferroelectric and antiferrodistortive properties of Bi1−x La x FeO3 thin films and nanoparticles by incorporating the gradient and surface energy terms that are strongly dependent on the shape, size, and preparation method.  

Editorial Summary
Multiferroics: The potential of bismuth ferrite 多铁性材料:铁酸铋的潜力 

本研究开发了一个理论方法,用来描述具有铁电性铁酸铋的复杂相图。多铁性是材料铁磁性和铁电性等多个性能偶合。铁酸铋或许是室温最佳多铁材料之一 

虽然其在室温多铁性具有多种用途,但其多铁性的基本物理机制仍然不太清楚。由白俄罗斯NAS实用材料科学研究中心和莫斯科电子技术研究所的Dmitry Karpinsky率领的国际研究团队,利用现有的实验数据构建了一种Landau-Ginzbur样热力学势,不仅能定量描述铁酸铋的已知行为,还能预测其新型中间相变构。 

A theoretical approach for describing the complex phase diagram of the multiferroic bismuth ferrite has been developed. Multiferroics are materials that exhibit multiple types of ferroic ordering, such as ferromagnetism and ferroelectricity, simultaneously. Bismuth ferrite is perhaps one of the best known of these as it exhibits multiferroicity at room temperature, making it useful for a range of applications, but the underlying physical mechanisms responsible for its multiferroic properties remains somewhat unclear. An international team of researchers led by Dmitry Karpinsky from the Scientific-Practical Materials Research Centre of NAS of Belarus and the Moscow Institute of Electronic Technology use existing experimental data to construct a Landau-Ginzbur-like thermodynamic potential that can not only provide a quantitatively description of bismuth ferrites known behavior, but also predicts new intermediate phases.

Effect of nonlinear and noncollinear transformation strain pathways in phase-field modeling of nucleation and growth during martensite transformation (非线性和非共线相变应变路径对相场模拟马氏体形核和生长的影响) 
Pengyang Zhao, Chen Shen, Ju Li & Yunzhi Wang
npj Computational Materials 3, Article number: 19 (2017)
doi:10.1038/s41524-017-0022-2
Published online:10 May 2017
Abstract| Full Text | PDF OPEN

摘要: 固体内的结构和化学组分的不均一性(杂质及缺陷)会产生内在的弹性场并进一步影响微观组织的演化;对该领域的研究,相场微弹理论已经发挥了重大作用。然而,传统相场微弹性理论中通常采用的关于本征相变应变张量和序参数间的线性和/或共线耦合关系排除了许多如原子计算所揭示的非线性相变路径。本研究采用更为一般的非线性和非共线相变应变路径,以此扩展现有相场微弹性理论,从而允许引入更为复杂的相变路径;该方法提供了一种多尺度建模方案,可将原子机制与总体动力学关联起来,从而更好地描述固态相变。作为实例,本研究探讨了一个一般的立方到四方的马氏体相变。结果表明,非线性相变路径可以显著改变形核和生长速率,并改变临界晶核的构型和激活能。本研究还发现,对于纯剪切马氏体相变,取决于实际相变路径,晶核以及奥氏体/马氏体界面可产生非零的远场静水压,从而可与其它晶体缺陷(例如点缺陷和背景张力/压缩场)展示出较传统理论预期更为复杂的相互作用。本文还进一步讨论了新理论应用在有关奥氏体/马氏体界面处的空穴聚集和共格界面处偏析现象研究的可能性。 

Abstract: The phase-field microelasticity theory has exhibited great capacities in studying elasticity and its effects on microstructure evolution due to various structural and chemical non-uniformities (impurities and defects) in solids. However, the usually adopted linear and/or collinear coupling between eigen transformation strain tensors and order parameters in phase-field microelasticity have excluded many nonlinear transformation pathways that have been revealed in many atomistic calculations. Here we extend phase-field microelasticity by adopting general nonlinear and noncollinear eigen transformation strain paths, which allows for the incorporation of complex transformation pathways and provides a multiscale modeling scheme linking atomistic mechanisms with overall kinetics to better describe solid-state phase transformations. Our case study on a generic cubic to tetragonal martensitic transformation shows that nonlinear transformation pathways can significantly alter the nucleation and growth rates, as well as the configuration and activation energy of the critical nuclei. It is also found that for a pure-shear martensitic transformation, depending on the actual transformation pathway, the nuclei and austenite/martensite interfaces can have nonzero far-field hydrostatic stress and may thus interact with other crystalline defects such as point defects and/or background tension/compression field in a more profound way than what is expected from a linear transformation pathway. Further significance is discussed on the implication of vacancy clustering at austenite/martensite interfaces and segregation at coherent precipitate/matrix interfaces. 

Editorial Summary
Structural transformation: a less linear approach (结构转变建模:不太线性的方法) 

美国研究人员开发了一种给固体晶体结构复杂变化建模的方法。来自俄亥俄州立大学的王云志教授及其同事所建的模型,能更精确地描述马氏体转变晶体结构的重排。尽管之前使用的相场微弹性理论为这种结构演化成功建模,但如同人们在用原子模拟时就已关注的那样,现有模型并没有纳入更加复杂的非线性相变路径。现在王教授及其同事扩展了相场微弹性理论,纳入了这些复杂路径。他们的研究表明,当考虑非线性耦合时,马氏体相的临界晶核构型和激活能均与传统相场微弹性理论所描述的存在显著差异。该模型有望进一步用于了解金属和陶瓷的结构转变过程。 

A method for modeling complex changes in the crystal structures of solids is developed by researchers in the USA. Yunzhi Wang from the Ohio State University and his colleagues’ model provides a more accurate description of crystal structure rearrangement during a phase change known as martensitic transformation. Even though this structural evolution has be modeled successfully using the phase-field microelasticity theory, the existing models do not incorporate some the more complex nonlinear transformation pathways that have been seen when using atomistic simulations. Wang and co-workers now extended phase-field microelasticity theory to include these complex pathways. They show that configuration and activation energies of a critical nucleus of the martensitic phase differ significantly when such nonlinear coupling is considered. This model has applications to understanding structural transformations in metals and ceramics.

Understanding and designing magnetoelectricheterostructures guided by computation: progresses, remaining questions, and perspectives (磁电异质结构的计算模拟和材料设计:进展、问题和展望)
Jia-Mian HuChun-Gang DuanCe-Wen Nan & Long-Qing Chen 
npj Computational Materials 3, Article number: 18 (2017)
doi:10.1038/s41524-017-0020-4
Published online:01 May 2017
Abstract| Full Text | PDF OPEN
摘要:磁电复合材料及异质结集磁性材料和介电材料的特性于一身,更重要的是,多种序参量之间的耦合会产生新的效应,例如,磁性材料中磁性序和介电材料中电极化序相互耦合产生磁电效应,即:磁场能和电场能可以在几乎零电流下实现相互转换,转换量大小决定了效应的强弱。复合材料和异质结中的磁电效应,通常由材料不同组元之间的界面进行磁、电和/或弹性能量的转换而实现,并可通过为每个材料组元选择合适的材料、形状及尺寸、及微结构而进行优化和设计。本文介绍了理论和计算指导下磁电耦合机理及磁电异质结设计两方面的最新进展,并讨论了磁电异质结方面一些有待解决的问题。我们编制了一个相对全面的实验数据集,用以总结块体和薄膜复合材料中的磁电耦合系数,并对磁电复合材料在材料微结构(介观)尺度上的数据驱动的计算设计作了展望。   

Abstract: Magnetoelectric composites and heterostructures integrate magnetic and dielectric materials to produce new functionalities, e.g., magnetoelectric responses that are absent in each of the constituent materials but emerge through the coupling between magnetic order in the magnetic material and electric order in the dielectric material.The magnetoelectric coupling in these composites and heterostructures is typically achieved through the exchange of magnetic, electric, or/and elastic energy across the interfaces between the different constituent materials, and the coupling effect is measured by the degree of conversion between magnetic and electric energy in the absence of an electric current. The strength of magnetoelectric coupling can be tailored by choosing suited materials for each constituent and by geometrical and microstructural designs. In this article, we discuss recent progresses on the understanding of magnetoelectric coupling mechanisms and the design of magnetoelectricheterostructures guided by theory and computation. We outline a number of unsolved issues concerning magnetoelectricheterostructures.We compile a relatively comprehensive experimental dataset on the magnetoelecric coupling coefficients in both bulk and thin-film magnetoelectric composites and offer a perspective on the data-driven computational design of magnetoelectric composites at the mesoscale microstructure level.

Facile measurement of single-crystal elastic constants from polycrystalline samples (以多晶样品测定单晶弹性常数的简便方法) 
Xinpeng Du & Ji-Cheng Zhao
npj Computational Materials
 3, Article number: 17 (2017)
doi:10.1038/s41524-017-0019-x
Published online:24 April 2017
Abstract| Full Text | PDF OPEN

Abstract: Elastic constants are among the most fundamental properties of materials. Simulations of microstructural evolution and constitutive/micro-mechanistic modeling of materials properties require elastic constants that are predominately measured from single crystals that are labor intensive to grow. A facile technique is developed to measure elastic constants from polycrystalline samples. The technique is based upon measurements of the surface acoustic wave velocities with the help of a polydimethylsiloxane film grating that is placed on a polished surface of a polycrystalline sample to confine surface acoustic waves that are induced by a femtosecond laser and measured using pump-probe time-domain thermoreflectance. Electron backscatter diffraction is employed to measure the crystallographic orientation along which the surface acoustic wave propagates in each grain (perpendicular to the polydimethylsiloxane grating). Such measurements are performed on several grains. A robust mathematical solution was developed to compute the surface acoustic wave velocity along any crystallographic orientation of any crystal structure with given elastic constants and density. By inputting various starting values of elastic constants to compute the surface acoustic wave velocities to match experimental measurements in several distinct crystallographic orientations using an optimization algorithm, accurate elastic constant values have been obtained from seven polycrystalline metal samples to be within 6.8% of single-crystal measurements. This new technique can help change the current scenario that experimentally measured elastic constants are available for only about 1% of the estimated 160,000 distinct solid compounds, not to mention the significant need for elastic constants of various solid solution compositions that are the base of structural materials.    

Editorial Summary
Mechanical properties: a simpler method for determining elasticity(机械性能:一种更简单的弹性测定方法)

美国科学家发明了一种可基于非完美样品测量材料弹性性能的方法。来自俄亥俄州立大学的Xinpeng DuJi-Cheng Zhao开发了一种用于基于多晶样品测量获得弹性常数的简易实验技术。材料的弹性或刚度在数学上可以用弹性常数来标定。目前测定材料弹性常数的主流实验方法都基于单晶样品。然而,单晶样品的制备过程相当费时费力,有时甚至根本制备不出来。与传统方法不同,DuZhao采用激光脉冲测定多晶样品中的所谓表面声波的速度,再结合他们发展的理论计算方法,即可根据材料的密度和测量出的声速确定材料的弹性常数。 

A method for measuring the elastic properties of a material even with a less than perfect sample is demonstrated by scientists in the USA. Xinpeng Du and Ji-Cheng (J.C.) Zhao from The Ohio State University develop a simple experimental technique for obtaining elastic constants from polycrystalline samples. A material’s elasticity or stiffness properties are mathematically summarized by a series of parameters known as its elastic constants. Most experimental techniques for measuring these elastic constants require samples that are single-crystals. But these can be time consuming to produce or perhaps even impossible. Instead, Du and Zhao measure the velocity of so-called surface acoustic waves produced on a polycrystalline sample using pulses of laser light. They then develop a robust mathematical framework that can determine elastic constants based on material density and the measured velocities.

 

摘要:弹性常数是材料最基本的特性之一。材料的微结构演化模拟和本构/微力学模型的建立都需要弹性常数作为输入。目前测定材料弹性常数的主流实验方法都要借助单晶样品,而单晶样品的制备相当费时费力。本研究开发了一种基于多晶样品测量弹性常数的简易技术。该技术基于表面声波波速测量:将聚二甲基硅氧烷膜光栅放置在多晶样品的抛光表面上用来限制表面声波,以飞秒激光激发表面声波,并利用泵浦时域热反射技术进行测量。利用电子背散射衍射测定出表面声波的传输方向(垂直于光栅刻线方向)与晶粒具体晶向的对应关系。利用上述方法对几个不同的晶粒进行了测量。同时发展了一种可靠的数学方法计算表面声波的波速,只要给定晶体的弹性常数和密度,即可计算出表面声波在任意晶体结构中沿任意晶向传播的速度。以不同的弹性常数为输入,计算表面声波波速,并通过优化算法将计算结果与7种不同的金属多晶样品的实验测量值进行匹配,由此获得了这些材料的弹性常数,其数值相比单晶测量值误差在6.8%以内。由于现有的弹性常数测量的方法具有很强的局限性,其仅可用来估测160,000种固体化合物中的约1%化合物的弹性常数,更无法满足作为结构材料基础的各种固溶体组合物弹性常数的测定需求,因此本研究提出的新技术有可能改变这一现状。 

A review: applications of the phase field method in predicting microstructure and property evolution of irradiated nuclear materials(综述:相场法在辐射核材料微观结构和性能演化预测中的应用)
Yulan Li, Shenyang Hu, Xin Sun & Marius Stan
npj Computational Materials
 3, Article number: 16 (2017)
doi:10.1038/s41524-017-0018-y
Published online:14 April 2017
Abstract| Full Text | PDF OPEN
摘要:核材料引起的强烈辐射和高温极端环境将使其自身和核燃料和结构材料发生复杂的微观结构变化。本文评价了相场法在预测辐射下核材料微结构演化方面的作用,以及在预测微结构演化对材料力学性能、热性能和磁性能影响方面的作用。首先概述了缺陷演化的重要物理机制,以及辐射下核材料微观结构演化模拟所存在的显着差距。然后介绍了有强大预测功能的相场法,并综述了该方法在放射核材料微结构和性能演变方面的应用。针对这些内容的回顾分析表明:(1)相场模型可以正确描述诸如与空间位置关联的生成、迁移、缺陷重组、辐射诱导的溶解、Soret效应、强界面能各向异性、弹性相互作用等重要现象;(2)相场法可以定性和定量地模拟2D3D微结构演化,包括辐射诱导的偏析、第二相成核、空隙迁移、空泡和气泡超晶格形成、间质环演化、水合物形成和晶粒生长;(3)相场法可正确预测微观结构与其性质之间的关系。本文最后专门讨论了相场法在应用于核材料辐射效应方面的优点和局限性。该文近期发表于npj Computational Materials 3, Article number: 16 (2017)doi:10.1038/s41524-017-0018-y  

Abstract: Complex microstructure changes occur in nuclear fuel and structural materials due to the extreme environments of intense irradiation and high temperature. This paper evaluates the role of the phase field method in predicting the microstructure evolution of irradiated nuclear materials and the impact on their mechanical, thermal, and magnetic properties. The paper starts with an overview of the important physical mechanisms of defect evolution and the significant gaps in simulating microstructure evolution in irradiated nuclear materials. Then, the phase field method is introduced as a powerful and predictive tool and its applications to microstructure and property evolution in irradiated nuclear materials are reviewed. The review shows that (1) Phase field models can correctly describe important phenomena such as spatial-dependent generation, migration, and recombination of defects, radiation-induced dissolution, the Soret effect, strong interfacial energy anisotropy, and elastic interaction; (2) The phase field method can qualitatively and quantitatively simulate two-dimensional and three-dimensional microstructure evolution, including radiation-induced segregation, second phase nucleation, void migration, void and gas bubble superlattice formation, interstitial loop evolution, hydrate formation, and grain growth, and (3) The Phase field method correctly predicts the relationships between microstructures and properties. The final section is dedicated to a discussion of the strengths and limitations of the phase field method, as applied to irradiation effects in nuclear materials.

A phase field model for snow crystal growth in three dimensions (三维雪晶生长的相场模型)
Gilles Demange, Helena Zapolsky, Renaud Patte & Marc Brunel
npj Computational Materials 3, Article number: 15 (2017)
doi:10.1038/s41524-017-0015-1
Published online:10 April 2017
Abstract| Full Text | PDF OPEN
摘要:
雪花的生长过程为自然界的中自发样式形成提供了一个令人着迷的实例。对这一现象的初步了解,已为各个活跃的科学领域所观察到的非平衡动力学现象,提出了重要见解,涉及从物理系统和化学系统中的图式形成,到生物学中的自组装问题。然而,目前的计算模型极少能成功地再现3D雪花的多样性,也没有建立模型参数与热力学定量之间的函数关系。本研究报告了一种改进的相场模型,能通过各向异性水分子附着、冷凝、表面扩散和各向异性的强表面张力,来描述冰-气相变的微妙,模拟雪花的各向异性、刻面生长和树突状生长。研究证实,该模型可从Nakaya固液相图中再现出最具挑战性的雪花3D形态的生长动力学,发现所再现的雪晶生长动力学与选择理论一致,与以前的实验观察一致。 

Abstract: Snowflake growth provides a fascinating example of spontaneous pattern formation in nature. Attempts to understand this phenomenon have led to important insights in non-equilibrium dynamics observed in various active scientific fields, ranging from pattern formation in physical and chemical systems, to self-assembly problems in biology. Yet, very few models currently succeed in reproducing the diversity of snowflake forms in three dimensions, and the link between model parameters and thermodynamic quantities is not established. Here, we report a modified phase field model that describes the subtlety of the ice vapour phase transition, through anisotropic water molecules attachment and condensation, surface diffusion, and strong anisotropic surface tension, that guarantee the anisotropy, faceting and dendritic growth of snowflakes.We demonstrate that this model reproduces the growth dynamics of the most challenging morphologies of snowflakes from the Nakaya diagram.We find that the growth dynamics of snow crystals matches the selection theory, consistently with previous experimental observations. 

Editorial Summary

Spontaneous patterns: Simulating snowflakes with a softer touch (自发模式:模拟有柔性触感的雪花)

采用通用界面模型计算复杂3D雪花生长为其他树状材料的模拟提供理论依据。当雪晶种子穿过大气不断捕获水分子时,雪晶体通过初始种子向外扩展而使水分子凝固。虽然大多数模拟方法都将这种不断增长的界面视为一个敏感的界限,但法国鲁昂大学的Gilles Demange和同事们报告说,可变换的模拟方法获得非常实用的结果。他们用相场模型技术,将雪花表面表示为冰和水蒸气混合的可移动薄层,用新的表面张力函数来表示各向异性结晶。该方法包括了模拟3D晶面的特殊算法,能使模型准确重现出基本的雪花形态,并可对各种气象条件下云中的冰水含量进行预测。 

A model that reproduces complex 3D snowflake growth using versatile interface descriptors may benefit other dendritic materials. Snow crystals solidify by expanding outward from an initial seed, capturing water molecules as they travel through the atmosphere.While most simulation methods treat this growing interface as a sharp boundary, Gilles Demange and colleagues from the University of Rouen in France report that a less rigid approach yields highly realistic results.Their technique uses a phase field model to represents the snowflake’s surface as a thin moveable layer where ice and vapour mix, and a new surface tension function to explain the anisotropic crystallisation. Including a special algorithm to simulate 3D crystal faceting enabled the model to duplicate essential snowflake morphologies and potentially predict ice water content in clouds under various weather conditions. 

 

A high-throughput framework for determining adsorption energies on solid surfaces(测定固体表面吸附能的高通量框架)
Joseph H. Montoya & Kristin A. Persson
npj Computational Materials 3, Article number: 14 (2017)
doi:10.1038/s41524-017-0017-z
Published online:30 March 2017
Abstract| Full Text | PDF OPEN
摘要:本研究提出了使用密度泛函理论来计算固体表面吸附能的高通量工作流程。采用Materials Project基础设施提供的开放源代码作为计算工具,我们将任意表面-被吸附底物之间不同构型的对称构建程序做了自动化处理。然后用这些算法以标准化、自动化方式构建和运行工作流程,以便在计算模拟过程中尽量减少用户的人为干预。为了验证这个的方法,本研究将该流程的计算结果与之前的实验和理论基准(来自固体表面化学吸附能CE27数据库)作了比较。这些基准能说明执行和管理200个以上密度函数理论计算任务如何可以降低为单次提交和后续分析。由于实现了吸附能的高效、高通量计算,本研究所提出的计算工具将可加快由理论指导的先进材料发现,及其在催化和表面科学领域的应用。 

Abstract: In this work, we present a high-throughput workflow for calculation of adsorption energies on solid surfaces using density functional theory. Using open-source computational tools from the Materials Project infrastructure, we automate the procedure of constructing symmetrically distinct adsorbate configurations for arbitrary slabs. These algorithms are further used to construct and run workflows in a standard, automated way such that user intervention in the simulation procedure is minimal. To validate our approach, we compare results from our workflow to previous experimental and theoretical benchmarks from the CE27 database of chemisorption energies on solid surfaces. These benchmarks also illustrate how the task of performing and managing over 200 individual density functional theory calculations may be reduced to a single submission procedure and subsequent analysis.By enabling more efficient high-throughput computations of adsorption energies, these tools will accelerate theory-guided discovery of advanced materials for applications in catalysis and surface science. 

Editorial Summary

Surface chemistry: an automatic sense of attraction(表面化学:引力的自动识别)

美国研究人员开发了一种自动化程序,能用来确定分子粘附在固体表面所需的能量。来自加州大学伯克利分校的劳伦斯伯克利国家实验室的Joseph Montoya和该大学的Kristin Persson开发了一种在任意表面上寻找吸附位点的算法。了解分子吸附所需的能量,对于确定电子器件和催化剂最佳材料来说至关重要。密度泛函理论可以预测吸附能量,但通常需要人们凭直觉来调整计算。由于表面和被吸附物的组合众多,选定最佳材料组合因而需要自动化方法。 MontoyaPersson采用Materials Project的开放源代码作为计算工具,为此提供了对任意表面-吸附物种间能进行高通量密度泛函理论计算的工作流程。 

An automated procedure for determining the energy required for a molecule to adhere to a surface is developed by researchers in the United States. Joseph Montoya from the Lawrence Berkeley National Laboratory and Kristin Persson from the University of California, Berkeley, introduce an algorithm for finding the adsorption sites on an arbitrary surface.Knowing the amount of energy required for molecular adsorption is crucial for identifying the best materials for use in electronics and catalysis. Density functional theory can predict adsorption energies but usually requires human intuition to tune the calculations.With so many combinations of surface and adsorbate, an automated method is required. Montoya and Persson use open-source computational tools from the Materials Project to present a workflow for performing high-throughput density functional theory calculations for arbitrary slabs and adsorbed species.

  

A three-dimensional polyhedral unit model for grain boundary structure in fcc metals(fcc金属晶界结构的三维多面体单元模型)
Arash Dehghan Banadaki & Srikanth Patala
npj Computational Materials
 3, Article number: 13 (2017)
doi:10.1038/s41524-017-0016-0
Published online:27 March 2017
Abstract| Full Text | PDF OPEN
摘要:发展真正的bottom-up模型计算多晶材料性能的最大挑战之一就是界面缺乏准确的结构-性能定量关系。作为分析这种关系的第一步,我们提出了一个“多面体单元”(polyhedral unit)模型,可以沿晶界的原子堆积几何结构特征进行分类。尽管无序系统中的原子结构一直是数十年来受到关注的问题,但由于其结构范围变化复杂,结构又可能具有基本宏观结晶学特征,所以晶界的几何结构分析特别具有挑战性。本研究提出了一种可以将原子间结构划分为三维多面体连接阵列的算法,从而提出了一种用于晶界分析的三维多面体单元模型。还提供了“点模式匹配”(point-pattern matching)算法,用于量化所观察的晶界多面体扭转。多面体单元模型能够准确描述高-Σ、耦合特征界面结构,因此它提供了一种几何结构方法,用来比较涵盖五参数晶体相空间的晶界结构。由于所获得的多面体单元限定了结构中的空隙,因而这样的分析提供了关于晶界内分离位点的有效信息。期望这种计算技术成为分析晶界结构的有力手段。本研究所提出的多面体单元模型算法适用于广泛材料体系的基本晶格结构分析。 

Abstract: One of the biggest challenges in developing truly bottom-up models for the performance of polycrystalline materials is the lack of robust quantitative structure–property relationships for interfaces. As a first step in analyzing such relationships, we present a polyhedral unit model to classify the geometrical nature of atomic packing along grain boundaries. While the atomic structure in disordered systems has been a topic of interest for many decades, geometrical analyses of grain boundaries has proven to be particularly challenging because of the wide range of structures that are possible depending on the underlying macroscopic crystallographic character. In this article, we propose an algorithm that can partition the atomic structure into a connected array of three-dimensional polyhedra, and thus, present a three-dimensional polyhedral unit model for grain boundaries. A point-pattern matching algorithm is also provided for quantifying the distortions of the observed grain boundary polyhedral units. The polyhedral unit model is robust enough to capture the structure of high-Σ, mixed character interfaces and, hence, provides a geometric tool for comparing grain boundary structures across the five-parameter crystallographic phase-space. Since the obtained polyhedral units circumscribe the voids present in the structure, such a description provides valuable information concerning segregation sites within the grain boundary. We anticipate that this technique will serve as a powerful tool in the analysis of grain boundary structure. The polyhedral unit model is also applicable to a wide array of material systems as the proposed algorithm is not limited by the underlying lattice structure. 

Editorial Summary

Polyhedral structures: Building blocks for metallic interfaces(多面体结构:金属界面的构件)

美国研究人员设计了一个模型来帮助了解诸如铝和铜等金属中晶体是如何堆积形成的机制。大多数金属形成多晶微结构,即它们由许多不同尺寸和取向的小晶体组成。在不同取向的晶界处,缺乏有序结构,难以对其性质进行建模。针对这些问题,北卡罗来纳州立大学的Arash BanadakiSrikanth Patala首先对这些界面结构与微观单元结构的关系作出了定量处理,开发一个三维模型,依据微结构中原子沿着无序区域堆积模式的几何结构进行分类。该模型虽然只在面心立方晶体上进行了测试,但也适用于其他有不同晶格结构体系。本方法是通过自下而上设计出所需性能的结构材料的第一步,也是关键一步。 

US researchers have designed a model to aid understanding of how crystals pack in metals such as aluminum and copper. Most metals form as polycrystalline microstructures, i.e., they are composed of small crystals of varying size and orientation. The lack of structural order, along the interfaces where crystals of different orientations meet, m it difficult to model their properties. Arash Banadaki and Srikanth Patala at North Carolina State University have taken the first step towards quantifying these relationships, by developing a three-dimensional model that classifies the geometrical nature of how atoms pack along these disordered regions in the microstructure. The model was tested on face-centered cubic crystals, but is also applicable to systems with different lattice structures. This is a key first step in the bottom-up design of structural materials with desired properties. 

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