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  《npj 計算材料學》是在線出版、完全開放獲取的國際學術期刊。發表結合計算模擬與設計的材料學一流的研究成果。本刊由中國科學院上海硅酸鹽研究所與英國自然出版集團(Nature Publishing Group,NPG)以伙伴關系合作出版。
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Delocalization of dark and bright excitons in flat-band materials and the optical properties of V2O5        
Vitaly Gorelov, Lucia Reining, Martin Feneberg, Rüdiger Goldhahn, André Schleife, Walter R. L. Lambrecht  & Matteo Gatti       
npj Computational Materials 8: 94 (2022)
doi.org/10.1038/s41524-022-00754-2
Published online: 28 April 2022
Abstract| Full Text | PDF OPEN

Abstract: The simplest picture of excitons in materials with atomic-like localization of electrons is that of Frenkel excitons, where electrons and holes stay close together, which is associated with a large binding energy. Here, using the example of the layered oxide V2O5, we show how localized charge-transfer excitations combine to form excitons that also have a huge binding energy but, at the same time, a large electron-hole distance, and we explain this seemingly contradictory finding. The anisotropy of the exciton delocalization is determined by the local anisotropy of the structure, whereas the exciton extends orthogonally to the chains formed by the crystal structure. Moreover, we show that the bright exciton goes together with a dark exciton of even larger binding energy and more pronounced anisotropy. These findings are obtained by combining first principles many-body perturbation theory calculations, ellipsometry experiments, and tight binding modeling, leading to very good agreement and a consistent picture. Our explanation is general and can be extended to other materials.

摘要: 在具有類原子局域電子的材料中,激子最簡單的圖像是Frenkel激子,其中電子和空穴緊密靠著,這與大的結合能有關。在這里,以層狀氧化物V2O5為例,我們展示了局域電荷轉移激發是如何結合形成激子的,這些激子具有巨大的結合能,但電子-空穴的距離同時也很大,我們解釋了這個看似矛盾的發現。激子離域的各向異性是由結構的局部各向異性決定的,而激子則正交地延伸到由晶體結構形成的鏈上。此外,我們發現明亮的激子是與一個具有更大結合能和更明顯各向異性的暗激子一起出現的。這些發現通過結合第一性原理多體微擾理論計算、橢圓偏振實驗和緊密結合模型得到,取得了非常好的一致性圖像。我們的解釋具有普適性且可以推廣到其他材料。

Editorial Summary

Intriguing bright and dark excitons inV2O5

It is common belief that the exciton binding energy is directly dependent on spatial localization. The classical Wannier and Frenkel textbook models describe, respectively, the limiting cases of weakly bound and delocalized excitons, typically found in ordinary semiconductors, and tightly bound and localized excitons, observed in molecular or noble gas solids. Recent development of two-dimensional (2D) materials have sparked the interest in exploring excitons that stand out from the conventional expectation. 2D materials usually have large exciton binding energies, irrespective of spatial extent, which can be rationalized as the consequence of reduced effective screening. However, there has been a long-standing controversy about whether strongly bound charge-transfer excitons can be considered Frenkel excitons. This work proposes an exciton model that explains the counter-intuitive anisotropy and delocalization of charge-transfer excitons. Prof. Gorelov and coworkers from Institut Polytechnique de Paris and coworkers, take V2O5 as a prototypical system to study how the localized charge-transfer excitations form an exciton by combing first-principles calculations, ellipsometry experiments and tight-binding model. As a flat-band material, V2O5 has intriguing excitons which contradict textbook expectations. Flat bands correspond to localized electronic states, and the exciton binding energy is very large. When the single-particle excitations that are mixed to form an exciton are charge-transfer excitations, the wave function of the exciton is delocalized, which shows an anisotropy determined by the local motif of the charge-transfer unit. In addition, they found that the dark and bright excitons are strongly bound in the gap. In the lowest dark and bright excitons, the electron density for a hole on a bridge oxygen extends perpendicular to the atomic chains along which electrons disperse. This work provides valuable guidelines for identifying materials where excitons exhibit properties tailored for specific needs.

編輯概述

V2O5材料中奇特的明暗激子

激子的結合能通常被認為與其空間位置有關。教科書上經典的 Wannier 和 Frenkel 模型分別描述了通常在普通半導體中觀察到的弱束縛(離域)激子和在分子或惰性氣體中觀察到的緊密束縛(局域)激子的極限情況。近年來二維材料的發展,引起了人們探索與傳統激子特性不一樣的激子系統。二維材料的激子結合能普遍很大,且與與空間位置無關,這通常被認為與低維材料的有效屏蔽有關。然而,關于是否可以將強束縛電荷轉移激子認為是 Frenkel 激子還一直存在爭議。本工作中提出了一個激子模型,成功解釋了電荷轉移激子的各向異性和離域性質。來自法國巴黎理工學院的Gorelov教授及其同事,以V2O5作為研究原型對象,結合第一性原理計算、橢偏實驗和緊束縛模型,研究了局部電荷轉移激發是如何形成激子的。V2O5作為平帶材料,其激子具有與傳統預期相矛盾的有趣特性:平帶對應于局部電子態,激子結合能非常大。當混合形成激子的單粒子激發具有鏡像對稱性的電荷轉移激發時,激子的波函數是離域的,并顯示出了由電荷轉移單元局部基序控制的各向異性。此外,他們還發現,明暗激子是一起出現在間隙中的,他們強烈的束縛在一起。在最低的明暗激子中,V2O5中橋氧上的空穴電子密度垂直于電子分散的原子鏈。這項工作為識別具有特定需求的激子的材料提供了有價值的指導。

Atomic coordination dictates vibrational characteristics and thermal conductivity in amorphous carbon        
Ashutosh Giri, Connor J. Dionne & Patrick E. Hopkins      
npj Computational Materials 8: 55 (2022)
doi.org/10.1038/s41524-022-00741-7
Published online: 4 April 2022
Abstract| Full Text | PDF OPEN

Abstract: We discuss the role of atomic coordination in dictating the vibrational characteristics and thermal conductivity in amorphous carbon. Our systematic atomistic simulations on amorphous carbon structures at varying mass densities show the significant role played by the ratio of sp2 to sp3 hybridized bonds in dictating the contributions from propagating (phonon-like) and non-propagating vibrational modes and their influence on the overall thermal conductivities of the structures. Specifically, our results show that as the concentration of sp3-bonded carbon atoms increases, the thermal conductivity can be increased by four fold, which is attributed to enhanced contributions from propagating modes in these amorphous structures. Our results shed more light into the role of atomic coordination on dictating heat transfer mechanisms in amorphous materials, and also provide a deeper understanding of the ability to tune the thermal conductivity of amorphous carbon structures through the control of the local atomic coordination.

摘要: 我們討論了原子配位在決定非晶碳的振動特性和熱導率中的作用。我們對不同質量密度的非晶碳結構進行了系統原子模擬,結果表明,sp2 與 sp3 雜化鍵的比率在決定傳播(類聲子)和非傳播振動模式的貢獻,及其對結構整體熱傳導的影響方面發揮了重要作用。具體來說,我們的結果表明,隨著 sp3 鍵合碳原子濃度的增加,熱導率可以增加四倍,這可歸因于這些非晶結構中傳播模式的貢獻增強。我們的研究結果進一步闡明了原子配位在決定非晶材料傳熱機制中的角色,并提供了對通過控制局部原子配位來調節非晶碳結構熱導率能力的更深入理解。

Editorial Summary

Thermal conductivity in amorphous carbon: atomic coordination

Diamond-like carbon is a class of amorphous carbon material that has attracted much attention over more than half a century due to its unique combination of properties that are tunable between those found in diamond and those in graphite. Depending on the sp3 content in amorphous carbon, the chemical and physical properties can be controlled over a wide range. In particular, there has been a considerable amount of interest in understanding thermal transport properties in amorphous carbon both from experimental and computational standpoints. Up to now, however, a systematic study focusing on the influence of relative fractions of sp3- and sp2-bonded carbons on the thermal transport properties of amorphous carbon structures is still missing. Moreover, it is also not clear what impact carbon hybridization has on the fundamental character of the different vibrational modes in amorphous carbon. This study discusses the role of atomic coordination in dictating the vibrational characteristics and thermal conductivity in amorphous carbon. A team led by Prof. Patrick E. Hopkins from University of Virginia, USA, has studied the role of carbon hybridization on the vibrational heat transfer mechanisms in amorphous carbon structures via systematic atomistic simulations. The results show the significant role played by the fraction of sp3-bonded carbon atoms in dictating the contributions from propagating (phonon-like) vibrational modes and their influence on the overall thermal conductivity. The study shows that as the concentration of sp3-bonded carbon atoms increases from ~10 to ~80% in our amorphous carbon structures, the thermal conductivity can be increased by four folds, which is due to the drastic increase in the contribution from propagating modes. For the amorphous carbon structure with the highest concentration of sp3-bonded carbon, the thermal conductivity can reach a record high value of 11?W?m?1?K?1, which is the highest thermal conductivity for any known amorphous solid till date. This study reveals the relationship between atomic coordination and the fundamental characteristics of the vibrational modes in amorphous carbon, thus opening an avenue to efficiently tune the thermal conductivity of these materials based on carbon hybridization. 

編輯概述

非晶碳熱導率:原子配位

類金剛石碳在半個多世紀以來一直備受關注。它是一種非晶碳材料,具有在金剛石和石墨之間可調節的獨特性能。根據非晶碳中的sp3含量,可以在很寬的范圍內控制其化學和物理特性。特別是針對非晶碳的熱傳輸特性,人們一直有著極大的興趣,也得到實驗和理論方面的長期研究。然而,針對sp3與sp2鍵合碳的比率對非晶碳結構的熱傳輸性質影響的系統研究至今缺乏。此外,碳雜化對非晶碳中不同振動模式的基本特征的影響仍不清楚。該研究討論了原子配位在決定非晶碳的振動特性和熱導率中的作用。來自美國弗吉尼亞大學的Patrick E. Hopkins教授領導的團隊,通過系統的原子模擬,研究了碳雜化對非晶碳結構中振動傳熱機制的作用。該研究結果表明,sp3鍵合碳原子的比例在決定傳播(類聲子)振動模式的貢獻及其對整體熱導率的影響方面發揮了重要作用。研究發現,隨著非晶碳結構中sp3鍵合碳原子的濃度從~10%增加到~80%,傳播模式的貢獻急劇增加,從而使熱導率可以增加四倍。對于具有最高濃度sp3鍵合碳的非晶碳結構,其熱導率可以達到創紀錄的11?W?m?1?K?1,這是迄今為止已知非晶固體的最高熱導率。該研究揭示了原子配位與非晶碳中振動模式的基本特征之間的關系,為基于碳雜化有效調節這些材料的熱導率開辟了一條途徑。

Dilute carbon in H3S under pressure        
Xiaoyu Wang, Tiange Bi, Katerina P. Hilleke, Anmol Lamichhane, Russell J. Hemley & Eva Zurek     
npj Computational Materials 8: 87 (2022)
doi.org/10.1038/s41524-022-00769-9
Published online: 27 April 2022
Abstract| Full Text | PDF OPEN

Abstract: Recently, room temperature superconductivity was measured in a carbonaceous sulfur hydride material whose identity remains unknown. Herein, first-principles calculations are performed to provide a chemical basis for structural candidates derived by doping H3S with low levels of carbon. Pressure stabilizes unusual bonding configurations about the carbon atoms, which can be six-fold coordinated as CH6 entities within the cubic H3S framework, or four-fold coordinated as methane intercalated into the H-S lattice, with or without an additional hydrogen in the framework. The doping breaks degenerate bands, lowering the density of states at the Fermi level (NF), and localizing electrons in C-H bonds. Low levels of CH4 doping do not increase NF to values as high as those calculated for Im3(_)m-H3S, but they can yield a larger logarithmic average phonon frequency, and an electron–phonon coupling parameter comparable to that of R3m-H3S. The implications of carbon doping on the superconducting properties are discussed.

摘要: 最近,研究人員測得了一種具有室溫超導性的碳質硫氫化物材料,但其本征結構還未知。在這里,我們通過第一性原理計算,為低碳摻雜 H3S 衍生的結構候選物提供了化學基礎。壓力穩定了碳原子周圍反常的鍵合構型,在框架中有或沒有額外的氫的情況下,碳原子可以作為立方 H3S 框架內的 CH6形成六倍配位,或者作為甲烷插入 H-S 晶格中形成四倍配位。摻雜打破了簡并能帶,降低了費米能級 (NF)處的態密度,并將電子局域在 C-H 鍵中。低濃度 CH4 摻雜不會將 NF 增加到與 Im3(_)m-H3S計算值一樣高的值,但它們可以產生更大的對數平均聲子頻率,并產生與 R3m-H3S 相當得電子 - 聲子耦合參數。本文討論了碳摻雜對超導特性的影響。

Editorial Summary

Superconducting phase of low-level C doped H3S: First-principles exploration

During the past decades, tremendous efforts have been made in the exploration of room temperature superconductors, and fruitful results have been obtained. Earlier studies predicted that hydrogen-rich compounds metallized under pressure could be phonon-mediated high-temperature superconductors, where synergy between experiment and theory has led to remarkable progress. One typical example is H3S, for which a superconducting critical temperature, Tc, of 203?K was reported near 150?GPa; Another example is carbonaceous sulfur hydride superconductor, which has a Tc of 288?K at 267?GPa. So far, a critical issue lies in the composition and structure of the phase, or phases that are responsible for the remarkable superconductivity. This aims to provide a chemical basis for structural candidates derived by doping H3S with low levels of carbon. A team led by Professor Eva Zurek from the Departments of Physics, Chemistry, and Earth and Environmental Sciences, University of Illinois Chicago and Professor Russell J. Hemley from the Department of Chemistry, State University of New York at Buffalo, explored the effects of carbon doping on the structural, electronic and superconducting properties of H3S. They systematically investigated the doping of H3S by 1.85–25% carbon that leads to a plethora of metastable phases, associated with the thermal and dynamic properties. They considered different types of substitution, including S being replaced by C, plus different amounts of hydrogen, where carbon can be either six-coordinated or four-coordinated to hydrogen. It was found that CH6 and CH4 form stable configurations within the dense solid in phases that are dynamically stable at the pressures studied experimentally. The doping breaks degenerate bands, lowers the density of states at the Fermi level and localizes electrons in C-H bonds, which affect the superconducting properties. 

編輯概述

低碳摻雜H3S的超導相:第一性原理探尋

室溫超導體在過去幾十年里得到廣泛研究,同時也取得到不少成果。前期,人們預測在壓力下金屬化的富氫化合物可能是聲子介導的高溫超導體,之后實驗與理論也取得了協同發展。其中一個典型的材料是H3S,其超導臨界溫度Tc在150?Gpa時達到203?K;后來,人們又報道了一種在267?GPa時Tc為 288?K 的碳質硫氫化物超導體。迄今一個關鍵問題是,導致碳質H3S超導性的相組成和結構猶未可知。來自伊利諾伊大學芝加哥分校物理、化學、地球與環境科學系的Eva Zurek與紐約州立大學布法羅分?;瘜W系的Russell J. Hemley等,通過第一性原理計算,為低碳摻雜 H3S 衍生的結構候選物提供了化學基礎。他們研究了碳摻雜對H3S幾何、電子結構和超導性能的影響。該研究系統地計算1.85–25%碳摻雜H3S系統的各種亞穩定結構,熱力學和動力學穩定性。作者考慮了S被C原子取代的不同類型結構,加上不同數量的氫,生成六配位或四配位碳原子。研究發現,在實驗研究的壓力下,CH6和CH4在致密固體中可以形成穩定的構型。此外,摻雜降低了費米能處的態密度,破壞了簡并度并使電子在碳氫鍵中局域化,這對超導特性有重要影響。

XGBoost model for electrocaloric temperature change prediction in ceramics        
Jie Gong, Sharon Chu, Rohan K. Mehta & Alan J. H. McGaughey    
npj Computational Materials 8: 140 (2022)
doi.org/10.1038/s41524-022-00826-3
Published online: 1 July 2022
Abstract| Full Text | PDF OPEN

Abstract: An eXtreme Gradient Boosting (XGBoost) machine learning model is built to predict the electrocaloric (EC) temperature change of a ceramic based on its composition (encoded by Magpie elemental properties), dielectric constant, Curie temperature, and characterization conditions. A dataset of 97 EC ceramics is assembled from the experimental literature. By sampling data from clusters in the feature space, the model can achieve a coefficient of determination of 0.77 and a root mean square error of 0.38?K for the test data. Feature analysis shows that the model captures known physics for effective EC materials. The Magpie features help the model to distinguish between materials, with the elemental electronegativities and ionic charges identified as key features. The model is applied to 66 ferroelectrics whose EC performance has not been characterized. Lead-free candidates with a predicted EC temperature change above 2?K at room temperature and 100?kV/cm are identified.

摘要: 建立了一個 eXtreme Gradient Boosting (XGBoost) 機器學習模型,用于根據陶瓷的成分(由 Magpie 元素特性編碼)、介電常數、居里溫度和表征條件來預測陶瓷的電卡 (EC) 溫度變化。從實驗文獻中構筑了 97 個 EC 陶瓷的數據集。通過從特征空間中的簇中采樣數據,該模型可以實現測試數據的決定系數為 0.77,均方根誤差為 0.38?K。特征分析表明,該模型捕獲了有效 EC 材料的已知物理特性。 Magpie 特征有助于模型區分材料,元素電負性和離子電荷被確定為關鍵特征。該模型應用于 66 種 EC 性能尚未表征的鐵電體。確定了在室溫下預測 EC 溫度變化高于 2?K 和 100?kV/cm 的無鉛候選物。

Editorial Summary

Difficulty to find electrocaloric ceramics? Machine learning will lead the way

The electrocaloric (EC) effect is the coupling temperature and entropy change of dielectric materials caused by the polarization change caused by the application or removal of the electric field. The EC cooling device may reach 60-70% of the Carnot coefficient of performance, which is more effective than the thermal electric device. Compared with the large magnetic field required by the magneto thermal cooling device, the large electric field required to operate the EC cooling device is easily generated. EC temperature change( Δ TEC) is a function of material, characterization temperature and applied electric field. Its size is usually large near the phase transition temperature and increases with the increase of the applied electric field. The key to construct EC cooling device is to find a large Δ TEC's materials. Identifying effective EC materials is a difficult task. In order to help find effective EC materials, the team of Professor Alan J. H. McGaughey from the Department of mechanical engineering of Carnegie Mellon University applied the data-driven method to build a machine learning (ML) model to predict the mechanical properties of ceramics according to the material composition, dielectric constant, Curie temperature and characterization conditions Δ TEC。 They established a limit gradient lifting (xgboost) model to predict the composition, dielectric constant, Curie temperature and characterization conditions of ceramic ferroelectric materials Δ TEC。 The data set was made up of available experiments Δ Tec measurements are combined. The model correctly identifies the known physical fields (i.e., the applied electric field and the difference between the characterization and Curie temperature) that cause large EC temperature changes. The model is applied to find effective EC materials from 66 kinds of ferroelectrics whose EC properties have not been characterized, and propose candidate materials for future experimental verification. The predictive power of the xgboost model indicates that the physics based data-driven approach is a promising way to study EC materials. 

編輯概述

電卡陶瓷找不到,機器學習來領道

電卡 (EC) 效應是施加或去除電場造成介電材料極化變化而引起的溫度和熵的耦合變化,EC 冷卻裝置比熱電裝置更有效,有可能達到卡諾性能系數的 60%-70%。與磁熱冷卻裝置所需的大磁場相比,運行 EC 冷卻裝置所需的大電場很容易產生。EC 溫度變化 (ΔEC) 是材料、表征溫度和外加電場的函數。它的大小通常在相變溫度附近較大,并且隨著施加的電場強度增加而增加。構建 EC 冷卻裝置的關鍵是找到具有較大ΔTEC的材料。但識別有效的 EC 材料是一項艱巨的任務。為了有效地尋找EC材料,來自美國卡內基梅隆大學機械工程系的Alan J. H. McGaughey教授團隊,應用數據驅動的方法來構建機器學習(ML) 模型,以根據材料成分、介電常數、居里溫度和表征條件來預測陶瓷的 ΔTEC。他們建立了一個極限梯度提升 (XGBoost) 模型,以根據陶瓷鐵電材料的成分、介電常數、居里溫度和表征條件來預測其 ΔTEC。該數據集由可用的實驗 ΔTEC測量值組合而成,其模型正確識別了導致較大 EC 溫度變化的已知物理場(即,施加的電場以及表征和居里溫度之間的差異)。應用該模型從66 種 EC 性能尚未表征的鐵電體中尋找有效的 EC 材料,并為未來的實驗驗證提出候選材料。XGBoost 模型的預測能力表明,基于物理的數據驅動方法是研究 EC 材料的有前途的路徑。

Superconductivity in antiperovskites        
Noah Hoffmann, Tiago F. T. Cerqueira, Jonathan Schmidt & Miguel A. L. Marques    
npj Computational Materials 8: 150 (2022)
doi.org/10.1038/s41524-022-00817-4
Published online: 13 July 2022
Abstract| Full Text | PDF OPEN

Abstract: We present a comprehensive theoretical study of conventional superconductivity in cubic antiperovskites materials with composition XYZ3 where X and Z are metals, and Y is H, B, C, N, O, and P. Our starting point are electron–phonon calculations for 397 materials performed with density-functional perturbation theory. While 43% of the materials are dynamically unstable, we discovered 16 compounds close to thermodynamic stability and with Tc higher than 5?K. Using these results to train interpretable machine-learning models, leads us to predict a further 57 (thermodynamically unstable) materials with superconducting transition temperatures above 5?K, reaching a maximum of 17.8?K for PtHBe3. Furthermore, the models give us an understanding of the mechanism of superconductivity in antiperovskites. The combination of traditional approaches with interpretable machine learning turns out to be a very efficient methodology to study and systematize whole classes of materials and is easily extendable to other families of compounds or physical properties.

摘要: 我們對立方反鈣鈦礦材料的常規超導性進行了全面的理論研究,其成分為 XYZ3,其中 X 和 Z 是金屬,Y 是 H、B、C、N、O 和 P。我們的出發點是對 397 種材料的電子-聲子計算用密度泛函微擾理論進行。雖然 43% 的材料是動態不穩定的,但我們發現了 16 種接近熱力學穩定性且 Tc 高于 5?K 的化合物。使用這些結果來訓練可解釋的機器學習模型,我們可以預測另外 57 種(熱力學不穩定)材料超導轉變溫度高于 5?K,PtHBe3 最高可達 17.8?K。此外,這些模型讓我們了解了反鈣鈦礦的超導機制。傳統方法與可解釋的機器學習相結合被證明是研究和系統化整個材料類別的一種非常有效的方法,并且很容易擴展到其他化合物或物理特性家族。

Editorial Summary

Power of Informatics: Performance Optimization of dye-sensitized solar cells

Perovskite is one of the widely studied ternary compounds and has been applied in many technical fields, such as photovoltaic, piezoelectric, magnetic, thermoelectric, laser, multiferroic and so on. One field where perovskite plays a key role is superconductivity. Copper oxide ceramics that maintain the highest transition temperature (TC) record belong to this family. In recent years, several other carbides, borides, even nitrides and oxide anti perovskite have been found to be superconductors, but their superconducting transformation mechanism is still controversial. Professor Miguel A. L. Marques, from Institut für Physik, Martin-Luther-Universit?t Halle-Wittenberg,, Germany, combined the standard method with the updated machine learning method to conduct a comprehensive theoretical study on the conventional superconductivity of cubic anti perovskite materials. It is not only to study the physical properties of a specific system, but also to understand the overall behavior of the entire compound family. Specifically, they used the density functional perturbation theory to calculate the electron phonon properties. For machine learning, the selected algorithm can not only predict the relevant physical properties (electron phonon coupling strength λ and average phonon frequency ω, But also can provide data interpretation. These models can clarify the superconducting mechanism of antiperovskite. The combination of traditional methods and interpretable machine learning has proved to be a very effective method for studying and systematizing the whole material class, and it is easy to extend to other compounds or physical property families. 

編輯概述

機器學習:反鈣鈦礦的超導機理研究

鈣鈦礦是被廣泛研究的三元化合物家族之一,在許多技術領域都有應用,例如光伏、壓電、磁性、熱電、激光、多鐵性等。鈣鈦礦具有關鍵作用的一個領域是超導性,保持最高轉變溫度(Tc)記錄的銅氧化物陶瓷就屬于這個家族。近年來發現其它幾種碳化物、硼化物,甚至氮化物和氧化物反鈣鈦礦被實驗證明是超導體,但是其超導轉變機理還存在爭議。來自德國馬丁路德?哈勒維騰貝格大學物理研究所的Miguel A. L. Marques教授團隊將標準方法與更新的機器學習方法結合使用,對立方反鈣鈦礦材料的常規超導性進行了全面的理論研究。不僅是研究特定系統的物理特性,而且是了解整個化合物家族的整體行為。具體來說,他們采用密度泛函微擾理論來計算電子 - 聲子特性。對于機器學習,選擇的算法不僅能夠預測相關的物理特性(電子-聲子耦合強度 λ 和平均聲子頻率 ω),而且還能夠提供數據的解釋。這些模型能夠明確反鈣鈦礦的超導機制。傳統方法與可解釋的機器學習相結合被證明是研究和系統化整個材料類別的一種非常有效的方法,并且很容易擴展到其他化合物或物理特性家族。

Photovoltaphores: pharmacophore models for identifying metal-free dyes for dye-sensitized solar cells         
Hadar Binyamin & Hanoch Senderowitz    
npj Computational Materials 8: 142 (2022)
doi.org/10.1038/s41524-022-00823-6
Published online: 04 July 2022
Abstract| Full Text | PDF OPEN

Abstract: Dye-sensitized solar cells (DSSCs) are cost-effective, sustainable, and versatile electricity producers, allowing them to be incorporated into a variety of devices. In this work, we explore the usage of pharmacophore modeling to identify metal-free dyes for DSSCs by means of virtual screening. Pharmacophore models were built based on experimentally tested sensitizers. Virtual screening was performed against a large dataset of commercially available compounds taken from the ZINC15 library and identified multiple virtual hits. A subset of these hits was subjected to DFT and time-dependent-DFT calculations leading to the identification of two compounds, TSC6 and ASC5, with appropriate molecular orbitals energies, favorable localization, and reasonable absorption UV–vis spectra. These results suggest that pharmacophore models, traditionally used in drug discovery and lead optimization, successfully predicted electronic properties, which are in agreement with the theoretical requirements for sensitizers. Such models may therefore find additional usages as modeling tools in materials sciences.

摘要: 染料敏化太陽能電池 (DSSC) 是具有成本效益、可持續且用途廣泛的電力供應單元,可以將它們整合到各種設備中。在本工作中,我們探索了使用藥效團模型通過虛擬篩選來識別 DSSC 的無金屬染料?;趯嶒灉y試的敏化劑建立藥效團模型。針對從 ZINC15 庫中獲取的大量商用化合物數據集進行虛擬篩選,并確定了多個虛擬靶點。對這些靶點的一個子集進行 DFT 和時間相關的 DFT 計算,從而鑒定出兩種化合物 TSC6 和 ASC5,它們具有適當的分子軌道能量、有利的定位和合理的吸收 UV-vis 光譜。這些結果表明,傳統上用于藥物發現和先導優化的藥效團模型成功地預測了電子特性,這與敏化劑的理論要求一致。因此,此類模型可能會在材料科學中作為建模工具找到其他用途。

Editorial Summary

Power of Informatics: Performance Optimization of dye-sensitized solar cells

Dye sensitized solar cells (DSSC) are cost-effective, sustainable and versatile power supply units that can be integrated into various devices. However, the prediction of microstructure and properties is still a difficult problem for the rapid development of materials. The team of Professor Hanoch senderowitz from the Department of chemistry of Bar-Ilan University in Israel developed a new method to identify potential candidates for metal free dyes for DSSC using 3D pharmacophore models. Pharmacophore models were constructed from datasets of experimentally tested dyes and then used to screen the inventory portion of the zinc15 database containing more than 13.8 ? m compounds to retrieve those structures that match the relevant pharmacophore characteristics. The pharmacophore model was established based on the sensitizers tested in the experiment. Virtual screening was performed on a large number of commercial compound datasets obtained from the zinc15 library, and multiple virtual targets were identified. DFT and time-dependent DFT calculations were performed on a subset of these targets, and two compounds tsc6 and asc5 were identified, which have appropriate molecular orbital energy, favorable localization and reasonable absorption UV Vis spectra. These results indicate that the pharmacophore model has the ability to identify dyes with good (predicted) DSSC properties, thus building an important bridge between the spatial arrangement and electronic properties of simple chemical moieties. Crossing this bridge extends the use of ligand based pharmacophore models beyond its chemical informatics / drug design, into the field of materials science with many potentially exciting applications.

編輯概述

信息學的威力:染料敏化太陽能電池性能優化 

染料敏化太陽能電池 (DSSC) 是具有成本效益、可持續且用途廣泛的電力供應單元,可以將它們整合到各種設備中。但是其微結構和性能預測仍是困擾材料快速開發的難題。來自以色列巴伊蘭大學化學系的Hanoch Senderowitz教授團隊開發了一種新方法,使用 3D 藥效團模型來識別用于 DSSC 的無金屬染料的潛在候選者。藥效團模型是根據實驗測試染料的數據集構建的,然后用于篩選包含超過 13.8?M 化合物的 ZINC15 數據庫的庫存部分,以檢索與相關藥效團特征匹配的那些結構?;趯嶒灉y試的敏化劑建立藥效團模型。針對從 ZINC15 庫中獲取的大量商用化合物數據集進行虛擬篩選,并確定了多個虛擬靶點。對這些靶點的一個子集進行 DFT 和時間相關的 DFT 計算,從而鑒定出兩種化合物 TSC6 和 ASC5,它們具有適當的分子軌道能量、有利的定位和合理的吸收 UV-vis 光譜。這些結果表明,藥效團模型識別具有良好(預測)DSSC 特性的染料的能力,從而在簡單化學部分的空間排列和電子特性之間構建了一座重要的橋梁。穿越這座橋將基于配體的藥效團模型的使用擴展到其化學信息學/藥物設計之外,進入具有許多潛在令人興奮應用的材料科學領域。

On the role of the microstructure in the deformation of porous solids         
Sansit Patnaik, Mehdi Jokar, Wei Ding & Fabio Semperlotti     
npj Computational Materials 8: 152 (2022)
10.1038/s41524-022-00840-5
Published online: 18 July 2022
Abstract| Full Text | PDF OPEN

Abstract: This study explores the role that the microstructure plays in determining the macroscopic static response of porous elastic continua and exposes the occurrence of position-dependent nonlocal effects that are strictly correlated to the configuration of the microstructure. Then, a nonlocal continuum theory based on variable-order fractional calculus is developed in order to accurately capture the complex spatially distributed nonlocal response. The remarkable potential of the fractional approach is illustrated by simulating the nonlinear thermoelastic response of porous beams. The performance, evaluated both in terms of accuracy and computational efficiency, is directly contrasted with high-fidelity finite element models that fully resolve the pores’ geometry. Results indicate that the reduced-order representation of the porous microstructure, captured by the synthetic variable-order parameter, offers a robust and accurate representation of the multiscale material architecture that largely outperforms classical approaches based on the concept of average porosity.

摘要: 本研究探討了微結構在確定多孔彈性連續體的宏觀靜態響應中所起的作用,并揭示了與微觀結構的配置密切相關的位置相關非局部效應的發生。然后,發展了一種基于變階分數階微積分的非局部連續統理論,以準確捕捉復雜的空間分布非局部響應。通過模擬多孔梁的非線性熱彈性響應來說明分數方法的顯著潛力。從精度和計算效率兩方面評估的性能與完全解析孔隙幾何形狀的高保真有限元模型直接對比。結果表明,由合成可變階參數捕獲的多孔微觀結構的降階表示提供了多尺度材料結構的穩健和準確的表示,該結構在很大程度上優于基于平均孔隙率概念的經典方法。

Editorial Summary

Light as a feather, strong as a rock: Design of porous materials

Porous materials can achieve low weight and high stiffness (high specific stiffness) at the same time. Naturally occurring porous materials include wood, marine shells and rocks. The pursuit of materials with high specific stiffness has long been the main pursuit of structural engineering, thus providing a revolutionary alternative to traditional materials such as alloys and composites. However, the research of porous materials is limited by technology and theory. At the technical level, the manufacture of porous materials is extremely challenging. At the theoretical level, it is still unclear how the size effect is generated from the underlying microstructure and affects the internal multi-scale response of materials. The team of Professor Fabio sempelotti from the school of mechanical engineering of Purdue University in the United States describes the internal nonlocal properties of porous solids by directly linking the size effect with the specific characteristics of porous microstructure. This method provides a solid physical foundation for the development of nonlocal continuum models with high accuracy and high computational efficiency. This study provides two key contributions to the physical understanding and modeling of porous media. First, it shows that porous solids exhibit location dependent nonlocal effects that cannot be ignored if accurate predictions are sought. Secondly, the nonlocal continuum theory which can capture these complex nonlocal effects is developed and tested numerically. The results show that this method provides a strict method to develop a physically consistent reduced order model of multi-scale systems, and its accuracy is comparable to that of a fully analytical 3D model. Although the results are proposed in the context of porous materials, the research framework can be extended to various applications with multi-scale characteristics, including but not limited to composite materials, building materials, seismology, biotechnology, etc..

編輯概述

輕如鴻毛、強如磐石:多孔材料的設計 

多孔材料能夠同時實現低重量和高剛度(高比剛度),天然存在的多孔材料包括木材、海洋貝殼和巖石等,追求具有極高比剛度的材料長期以來一直是結構工程的主要追求,從而為合金和復合材料等傳統材料提供了變革性的替代方案。但目前多孔材料的研究受限于技術和理論方面。在技術層面上,多孔材料的制造極具挑戰性。在理論層面上,對尺寸效應如何從底層微觀結構中產生并影響材料的內在多尺度響應的機理仍然不清楚。來自美國普渡大學機械工程學院的Fabio Semperlotti教授團隊,通過將尺寸效應與多孔微觀結構的特定特征直接聯系起來,來描述多孔固體的內在非局部性質。這種方法為開發高精度和計算效率高的非局部連續統模型提供了堅實的物理基礎,這項研究為多孔介質的物理理解和建模提供了兩個關鍵貢獻。首先,它表明多孔固體表現出與位置相關的非局部效應,如果尋求準確的預測,就不能忽視這些效應。其次,開發了能夠捕捉這些復雜的非局部效應的非局部連續統理論并進行了數值測試。作者的研究提供了一種嚴格的方法來開發物理一致的多尺度系統降階模型,其精度可與完全解析的 3D 模型相媲美。雖然結果是在多孔材料的背景下提出的,但本研究框架可以擴展到具有多尺度特征的各種應用,包括但不限于復合材料、建筑材料、地震學、生物技術等。

High-throughput computation and structure prototype analysis for two-dimensional ferromagnetic materials              
Zhen-Xiong Shen, Chuanxun Su & Lixin He   
npj Computational Materials 8: 132 (2022)
doi.org/10.1038/s41524-022-00813-8
Published online: 23 June 2022

AbstractWe perform high-throughput first-principles computations to search the high Curie temperature (TC) two-dimensional ferromagnetic (2DFM) materials. We identify 79 2DFM materials and calculate their TC, in which Co2F2 has the highest TC = 541 K, well above the room temperature. The 79 2DFM materials are classified into different structural prototypes according to their structural similarity. We perform sure independence screening and sparsifying operator (SISSO) analysis to explore the relation between TC and the material structures. The results suggest that the 2DFM materials with shorter distance between the magnetic atoms, larger local magnetic moments and more neighboring magnetic atoms are more likely to have higher TC.

摘要: 我們開展了基于第一性原理方法的高通量計算,搜索具有高居里溫度的二維鐵磁材料。我們篩選出了79個二維鐵磁材料,其中Co2F2具有最高的居里溫度,為541開爾文,遠高于室溫。為了研究居里溫度與材料結構的關系,我們根據其結構相似性,將這79個二維鐵磁材料分為不同的結構原型。我們使用壓縮感知方法分析了居里溫度和材料結構之間的關系,發現當材料中磁性原子間的距離更短、局域磁矩更大和具有更多的近鄰磁性原子時,更可能具有高的居里溫度。

Editorial Summary

2D ferromagnetic material working under high temperature: Based on?

Two dimensional (2D) systems were once considered as lacking long-range ferromagnetic order at finite temperatures. Recently, several two-dimensional ferromagnetic (2DFM) materials have been found in experiments, which has attracted extensive attention. 2DFM materials may have a wide range of applications, but at present, only few of them have been synthesized, and their Curie temperatures are very low. It is challenging to find 2DFM materials with high Curie temperature. This study identified 79 2DFM materials through high-throughput first-principles calculations, of which Co2F2 has a Curie temperature of 541 Kelvin, much higher than room temperature. The relationship between Curie temperature and material structure is also analyzed. Recently, the team led by Prof. He, Lixin from the University of science and technology of China calculated the phase diagrams and Curie temperatures of 79 2DFM materials, via the first-principles linear response theory and Monte Carlo simulations. In order to study the relationship between Curie temperature and material structure, the authors carried out cluster analysis on these two-dimensional materials, and obtained 11 structural prototypes with similar structures; The empirical estimation formulas of Curie temperature and structural parameters of two-dimensional magnetic materials are obtained by the Sure Independence Screening and Sparsifying Operator (SISSO) method. It suggests that smaller magnetic atom spacing, larger local magnetic moment and more adjacent magnetic atoms (e.g., structures with multiple magnetic layers) will make the 2DFM materials have higher Curie temperature.

編輯概述

具有什么結構特征的二維鐵磁材料在更高溫度下還保持鐵磁性?

二維系統一度被認為在有限溫度下不存在長程鐵磁序。近期實驗研究陸續發現了幾種在有限溫度下仍具有鐵磁性的二維材料,引起了廣泛關注。二維鐵磁材料有廣泛的應用前景,但是目前合成的二維鐵磁材料還不多,且居里溫度較低。尋找到高居里溫度二維鐵磁材料具有一定挑戰性。最近來自中國科學技術大學的何力新教授團隊,搜集了文獻和數據庫中大量的二維材料,并通過高通量計算尋找二維鐵磁材料。他們采用基于第一性原理的線性響應理論計算了磁交換作用,并通過蒙特卡洛模擬計算材料的磁性相圖和居里溫度,最終確認了79個二維鐵磁材料,其中Co2F2具有541開爾文的居里溫度,遠高于室溫。為了研究居里溫度與材料結構的關系,作者對這些二維材料進行了聚類分析,得到了結構相似的11個結構原型;借助壓縮感知分析方法得到了二維磁性材料居里溫度與結構參數的經驗估值公式。該研究認為較小的磁性原子間距、較大的局域磁矩和更多的近鄰磁性原子(如具有多層磁性原子的結構)會使二維鐵磁材料擁有更高的居里溫度。

Dynamical phase-field model of coupled electronic and structural processes              
Tiannan Yang & Long-Qing Chen   
npj Computational Materials 8: 130 (2022)
doi.org/10.1038/s41524-022-00820-9
Published online: 22 June 2022
Abstract| Full Text | PDF OPEN

AbstractMany functional and quantum materials derive their functionality from the responses of both their electronic and lattice subsystems to thermal, electric, and mechanical stimuli or light. Here we propose a dynamical phase-field model for predicting and modeling the dynamics of simultaneous electronic and structural processes and the accompanying mesoscale pattern evolution under static or ultrafast external stimuli. As an illustrative example of application, we study the transient dynamic response of ferroelectric domain walls excited by an ultrafast above-bandgap light pulse. We discover a two-stage relaxational electronic carrier evolution and a structural evolution containing multiple oscillational and relaxational components across picosecond to nanosecond timescales. The phase-field model offers a general theoretical framework which can be applied to a wide range of functional and quantum materials with interactive electronic and lattice orders and phase transitions to understand, predict, and manipulate their ultrafast dynamics and rich mesoscale evolution dynamics of domains, domain walls, and charges.

摘要: 許多功能材料與量子材料的功能來源于材料的電子與晶格兩個子系統對于熱、電、機械、光刺激等的共同響應。本文提出一種用于預測與模擬電子、結構的同步動態過程以及相應的介觀尺度圖案演化的動力學相場模型。作為應用范例,本文研究了鐵電疇壁在高于帶隙光脈沖激發下的暫態動力學響應。研究發現,系統的動態過程包含了兩階段弛豫型電子、空穴演化過程,以及由多個震蕩型與弛豫型部分組成的結構演化過程,跨越了皮秒至納秒級別時間范圍。此模型可廣泛應用于具有電子序、結構序與電子相變、結構相變相互作用的多種類別的功能材料與量子材料,為理解、預測、控制材料的超快動態過程以及包含疇、疇壁、電荷等的介觀尺度演化的豐富信息提供了普適的理論框架。

Editorial Summary

Coupled electronic and lattice processes: A theoretical model for the nanoscale

The functionalities of a vast majority of functional materials are directly determined from the responses of both of their lattice and electron subsystems to external thermal, mechanical, and electromagnetic stimuli. Dynamical interactions among charge, orbit, and lattice degrees of freedom in these materials can give rise to coupled electronic and structural patterns and dynamical processes. The ability to theoretically predict and understand the coupled electronic and structural dynamics of materials is essential for both fundamental science and practical applications. A team led by Prof. Long-Qing Chen from the Department of Materials Science and Engineering, The Pennsylvania State University, USA, developed a novel dynamical phase-field model for predicting simultaneous electronic and structural processes and the accompanying evolution dynamics of nanoscale patterns, and predicted the light-excited charge and structural dynamics of ferroelectric domains for the first time. The work discovered a two-stage electronic carrier relaxation around a domain wall with a prolonged carrier lifetime by several orders of magnitude and a transient strain response containing several oscillational and relaxational components across picosecond-to-nanosecond timescales, providing useful theoretical insights on the rich simultaneous evolution dynamics of domains, domain walls, and charges. The work offers a general theoretical framework which can be applied to a wide range of functional materials with interactive electronic and lattice orders for understanding, predicting, and manipulating their dynamics and functionalities.

編輯概述

電子與晶格的耦合演化:納米尺度理論模型

材料中的晶格系統與電子系統會對熱、力、電磁等各種外界激勵產生靜態或動態的響應,兩個子系統的共同響應直接決定了大多數功能材料的性能。而電荷、軌道、晶格等的動態相互作用,可進一步引發材料中電子與結構層面的納米尺度圖案及動力學過程的相互耦合。如何理論預測與理解電子與晶格于納米尺度下的耦合動態過程,是研究材料動力學特性的關鍵。來自美國賓夕法尼亞州立大學材料科學與工程系的Long-Qing Chen教授團隊提出了一種新型的動力學相場理論模型,該方法可模擬電子與晶格共同參與的納米尺度微結構演化動力學,并首次理論預測了鐵電疇的電荷與晶格系統在光學激發下的超快動態過程。研究顯示,疇壁附近的電子、空穴濃度呈現兩階段弛豫型響應,載流子壽命延長了數個數量級,而應變呈現由多個震蕩型與弛豫型部分組成的復雜響應,響應過程跨越皮秒至納秒級別時間范圍,揭示了疇結構、疇壁、電荷共同演化的豐富信息。該研究為多種功能材料中的電子與晶格序的動態耦合提供了普適的理論工具,以理解、預測、并控制材料的動力學行為與功能。

Anisotropic Dzyaloshinskii-Moriya interaction protected by D2d crystal symmetry in two-dimensional ternary compound              
Yonglong Ga, Qirui Cui, Yingmei Zhu, Dongxing Yu, Liming Wang, Jinghua Liang & Hongxin Yang   
npj Computational Materials 8: 128 (2022)
doi.org/10.1038/s41524-022-00809-4
Published online: 08 June 2022
Abstract| Full Text | PDF OPEN

AbstractMagnetic skyrmions, topologically protected chiral spin swirling quasiparticles, have attracted great attention in fundamental physics and applications. Recently, the discovery of two-dimensional (2D) van der Waals (vdW) magnets have aroused great interest due to their appealing physical properties. Moreover, both experimental and theoretical works have revealed that isotropic Dzyaloshinskii–Moriya interaction (DMI) can be achieved in 2D magnets or ferromagnet-based heterostructures. However, 2D magnets with anisotropic DMI haven’t been reported yet. Here, via using first-principles calculations, we unveil that anisotropic DMI protected by D2d crystal symmetry can exist in 2D ternary compounds MCuX2 (M: 3d transition metal (TM), X: group VIA). Interestingly, by using micromagnetic simulations, we demonstrate that ferromagnetic (FM) antiskyrmions, FM bimerons, antiferromagnetic (AFM) antiskyrmions, and AFM bimerons can be realized in the MCuX2 family. Our discovery opens up an avenue to creating antiskyrmions and bimerons with anisotropic DMI protected by D2d crystal symmetry in 2D magnets.

摘要: 磁斯格明子作為一種具有拓撲保護的手性自旋螺旋準粒子,在基礎物理和應用中都引起了廣泛的關注。近年來,二維(2D)范德華磁體(vdW)的發現由于其誘人的物理特性引起了人們的極大興趣。此外,實驗和理論工作都揭示了二維磁體或鐵磁體基異質結構中可以實現各向同性Dzyaloshinskii-Moriya相互作用(DMI)。然而,具有各向異性DMI的二維磁體卻罕有報道。本文通過第一性原理計算,揭示了二維三元化合物MCuX2 (M: 3d過渡金屬(TM),X: VIA族)中存在受D2d晶體對稱性保護的各向異性DMI。有趣的是,通過微磁模擬,我們證明了在MCuX2家族中可以實現鐵磁(FM)反磁斯格明子、FM雙半子、反鐵磁(AFM)反磁斯格明子和AFM雙半子。我們的發現為創造具有各向異性DMI的反磁斯格明子和雙半子開辟了一條途徑,這些DMI在二維磁體中受到D2d晶體對稱性的保護。

Editorial Summary

Anti-topological spin textures are realized in two-dimensional ternary compounds protected by D2d crystal symmetry

Due to topological property, nano size and low drive current density of magnetic skyrmions make it an ideal information carrier for the next generation of spintronic storage or logic devices, such as orbital memory, reconfigurable logic gates, artificial neural devices for quantum computing with ultra-high density and low energy consumption of quantum bits. Recent work has revealed the realization of isotropic DMI Ne ?e ?l-type magnetic skyrmion, such as Cr(I,X)3, CrN and WTe2/Fe3GeTe2, in two-dimensional magnets with long range magnetic orderings. However, topological chiral magnetic structures with anisotropic DMI have not been reported in two-dimensional magnets. A team led by Prof. Hongxin Yang team From Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, via using first-principles calculations and atomistic spin model simulations confirm the anisotropic ferromagnetic (FM) skyrmions, FM bimerons, antiferromagnetic (AFM) skyrmions and AFM bimerons can be realized in layered van der Waals magnet MCuX2 (M: 3D Transition Metal (TM), X: VIA).

編輯概述

D2d晶體對稱保護的二維三元化合物中實現反拓撲自旋結構

磁斯格明子的拓撲保護、納米尺寸大小且驅動電流密度低的特性,使得其成為下一代自旋電子學存儲或邏輯器件的理想信息載體,如軌道存儲器、可重構邏輯門、人工神經元器件和用于量子計算的超高密度和低能耗的量子比特。新近發現二維(2D)長程磁序的磁體中可實現各項同性的Néel型斯格明子,如Mn(XY), Cr(X,Y) 以及WTe2/Fe3GeTe2等。然而,具有各向異性的拓撲手性磁結構還沒有在二維磁體中得到證實。來自中國科學院寧波材料科學與工程技術研究所的楊洪新研究員團隊,基于第一性原理計算和原子級自旋模擬,證實了各向異性的鐵磁斯格明子、雙半子和反鐵磁反斯格明子、雙半子可出現在層狀單層范德瓦爾斯磁體MCuX2(M: 3d過渡金屬(TM),X: 第六主族)中。此外,該研究還揭示了在連續的應力和溫度變化下,單層VCuSe2的磁參數和手性磁結構的尺寸也將發生明顯的改變,而且這種反磁斯格明子可以穩定在數百K的溫度下。該研究對于未來范德瓦爾斯材料和自旋電子學器件的研究具有重要價值。

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