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Bias-dependent surface stress by density functional theory combined with the effective screening medium method

Physical Review B 2024年第15期110卷 155409页

作者： Satoshi Hagiwara Shoji Ishibashi Minoru Otani Center for Computational Sciences Research Center for Computational Design of Advanced Functional Materials (CD-FMat)

We investigated the surface stress at an Al(111) electrode surface under a finite bias voltage using first-principles density functional theory combined with the effective screening medium (ESM) method. The surface stress depends quadratically on the bias voltage, whose profile has a maximum value at a finite voltage and a curvature corresponding to the capacitance obtained from the relationship between the excess charge and the electrode voltage. These features are consistent with the results of the thermodynamics at the electrode surface and previous experiments. The results of the layer-resolved local stress show that the bias dependence of the local stress correlates with the excess charge distribution from the outermost layer to the inner layer; the local stresses at the outermost and inner layers show parabolic and linear voltage dependences, respectively. Thus, the capacitance term of the macroscopic stress mainly originates from the outermost layer, and the contribution of the inner-layer stress is understood by the strain derivative of the excess charge. The stress analysis method with ESM is significant for modeling and understanding the surface stress at the electrode surface under a bias voltage.

关键词： Capacitance Electrochemical properties First-principles calculations Surface & interfacial phenomena Surfaces Density functional theory

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Effect of solid-solution strengthening on deformation mechanisms and strain hardening in medium-entropy V_(1-x)Cr_(x)CoNi alloys

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Journal of materials Science & Technology 2022年第13期108卷 270-280页

作者： Hyun Chung Dae Woong Kim Woo Jin Cho Heung Nam Han Yuji Ikeda Shoji Ishibashi Fritz Körmann Seok Su Sohn Department of Materials Science and Engineering Korea UniversitySeoul 02841South Korea Center for High Entropy Alloys Pohang University of Science and TechnologyPohang 37673South Korea Department of Materials Science and Engineering and Research Institute of Advanced Materials Seoul National UniversitySeoul 08826South Korea Institute for Materials Science University of StuttgartPfaffenwaldring 55Stuttgart 70569Germany Computational Materials Design Max-Planck-Institut für Eisenforschung GmbHMax-Planck-Strabe 1Düsseldorf 40237Germany Research Center for Computational Design of Advanced Functional Materials(CD-Fmat) National Institute of Advanced Industrial Science and Technology(AIST)TsukubaIbaraki 305-8568Japan Department of Materials Science and Engineering Delft University of TechnologyMekelweg2Delft 2628 CDthe Netherlands

High-and medium-entropy alloys(HEAs and MEAs)possess high solid-solution *** investigations have been conducted on its impact on yield strength,however,there are limited reports regarding the relation between solid-solution strengthening and strain-hardening *** addition,no attempt has been made to account for the dislocation-mediated plasticity;most works focused on twinning-or transformation-induced plasticity(TWIP or TRIP).In this work we reveal the role of solidsolution strengthening on the strain-hardening rate via systematically investigating evolutions of deformation structures by controlling the Cr/V ratio in prototypical V_(1-x)Cr_(x)CoNi *** the TWIP of CrCoNi with the dislocation slip of V_(0.4)Cr_(0.6)CoNi,the hardening rate of CrCoNi was superior to slip-band refinements of V_(0.4)Cr_(0.6)CoNi due to the dynamic Hall-Petch ***,as V content increased further to V_(0.7)Cr_(0.3)CoNi and VCoNi,their rate of slip-band refinement in V_(0.7)Cr_(0.3)CoNi and VCoNi with high solid-solution strength surpassed that of *** it is generally accepted in conventional alloys that deformation twinning results in a higher strain-hardening rate than dislocation-mediated plasticity,we observed that the latter can be predominant in the former under an activated huge solid-solution strengthening *** high solid-solution strength lowered the cross-slip activation and consequently retarded the dislocation rearrangement rate,i.e.,the dynamic *** delay in the hardening rate decrease,therefore,increased the strain-hardening rate,results in an overall higher strain-hardening rate of V-rich alloys.

关键词： Medium-entropy alloy Tensile property Solid-solution strength Strain-hardening rate Stacking fault energy

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Machine-learning potential for phonon transport in AlN with defects in multiple charge states

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Physical Review materials 2025年第3期9卷 034601-034601页

作者： Ying Dou Koji Shimizu Jesús Carrete Hiroshi Fujioka Satoshi Watanabe Institute of Industrial Science The University of Tokyo 4-6-1 Komaba Meguro Tokyo 153-8505 Japan Department of Materials Engineering The University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-8656 Japan Research Center for Computational Design of Advanced Functional Materials (CD-FMat) National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Central 2 1-1-1 Umezono Tsukuba Ibaraki 305-8568 Japan Instituto de Nanociencia y Materiales de Aragón (INMA) CSIC-Universidad de Zaragoza Zaragoza 50009 Spain

Understanding phonon transport properties in defect-laden AlN is important for their device applications. Here, we construct a machine-learning potential to describe phonon transport with ab initio accuracy in pristine and defect-laden AlN, following the template of Behler-Parrinello-type neural network potentials (NNPs) but extending them to consider multiple charge states of defects. The high accuracy of our NNP in predicting second- and third-order interatomic force constants is demonstrated through calculations of phonon bands, three-phonon anharmonic, phonon-isotope and phonon-defect scattering rates, and thermal conductivities. In particular, our NNP accurately describes the difference in phonon-related properties among various native defects and among different charge states of the defects. They reveal that the phonon-defect scattering rates induced by VN3+ are the largest, followed by VAl3−, and that VN1+ is the least effective scatterer. This is further confirmed by the magnitude of the respective depressions of the thermal conductivity of AlN. Our findings reveal the significance of the contribution from structural distortions induced by defects to the elastic scattering rates. The present work shows the usefulness of our NNP scheme to cost-efficiently study phonon transport in partially disordered crystalline phases containing charged defects.

关键词： Elastic scattering

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Analysis of molten metal spreading and solidification behaviors utilizing moving particle full-implicit method

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Frontiers in Energy 2021年第4期15卷 959-973页

作者： Ryo YOKOYAMA Masahiro KONDO Shunichi SUZUKI Koji OKAMOTO Department of Nuclear Engineering and Management The University of Tokyo7-3-1 HongoBunkyo-kuTokyo 113-8656Japan Research Center for Computational Design of Advanced Functional materials(CD-FMat) Department of Materials and ChemistryNational Institute of Advanced Industrial Science and Technology(AIST)Central 21-1-1UmezonoTsukubaIbaraki 305-8568Japan Institute of Engineering Innovation School of EngineeringThe University of Tokyo7-3-1 HongoBunkyo-kuTokyo 113-8656Japan Nuclear Professional School The University of Tokyo2-22 ShirakataTokai-muraIbaraki 319-1188Japan

To retrieve the fuel debris in Fukushima Daiichi Nuclear Power Plants(1F),it is essential to infer the fuel debris *** particular,the molten metal spreading behavior is one of the vital phenomena in nuclear severe accidents because it determines the initial condition for further accident scenarios such as molten core concrete interaction(MCCI).In this study,the fundamental molten metal spreading experiments were performed with different outlet diameters and sample amounts to investigate the effect of the outlet for spreading-solidification *** the numerical analysis,the moving particle full-implicit method(MPFI),which is one of the particle methods,was applied to simulate the spreading *** the MPFI framework,the melting-solidification model including heat transfer,radiation heat loss,phase change,and solid fraction-dependent viscosity was developed and *** addition,the difference in the spreading and solidification behavior due to the outlet diameters was reproduced in the *** simulation results reveal the detailed solidification procedure during the molten metal *** is found that the viscosity change and the solid fraction change during the spreading are key factors for the free surface condition and solidified ***,it is suggested that the MPFI method has the potential to simulate the actual nuclear melt-down phenomena in the future.

关键词： molten metal spreading solidification particle method severe accident fuel debris decommissioning

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Electronic, adsorption, and hydration structures of water-contained Na-montmorillonite and Na-beidellite through the first-principles method combined with the classical solution theory

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Physical Review materials 2022年第2期6卷 025001-025001页

作者： Satoshi Hagiwara Yasunobu Ando Yuta Goto Susumu Shinoki Minoru Otani Center for Computational Sciences University of Tsukuba 1-1-1 Tenno-dai Tsukuba Ibaraki 305-8577 Japan Research Center for Computational Design of Advanced Functional Materials (CD-FMat) National Institute of Advanced Industrial Science and Technology (AIST) 1-1-1 Umezono Tsukuba Ibaraki 305-8568 Japan Iwaki Laboratory Kunimine Industries Co. Ltd. 23-5 Kuidesaku Jobanshimofunao-machi Iwakishi Fukushima 972-8312 Japan

We investigated the electronic and hydration structures of montmorillonite (MMT) and beidellite (BEI) using a first-principles method combined with classical solution theory. Both MMT and BEI belong to a family of clay minerals with a layered structure containing water molecules and cations in the interlayer. First, we optimized the number of accumulated water molecules in the interlayer space and found the present results to be in reasonable agreement with previous experiments. Next, we refined the positions of the cations to determine the most stable structure based on the adsorption energy of the clay layers. We found that the cations in the interlayer stably adsorb to the clay layers and the most stable adsorption site is the center of the six-membered ring. The hydration structure strongly depends on the cation adsorption structure based on the charge density distribution of the water. In contrast, the electronic state is weakly dependent on the adsorption structure because of its insulating electronic structure. Therefore, our results strongly suggest that the physical properties of MMT and BEI arise from changes in the hydration structure induced by cation adsorption/desorption.

关键词： Charge Electronic structure Electrostatic interactions Van der Waals interaction Clay gels Liquid-solid interfaces Density functional theory

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Cover Feature: The Peptide Bond: Resonance Increases Bond Order and Complicates Fragmentation (ChemPhysChem 14/2024)

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ChemPhysChem 2024年第14期25卷

作者： Dr. Dmitri G. Fedorov Research Center for Computational Design of Advanced Functional Materials (CD-FMat) National Institute of Advanced Industrial Science and Technology (AIST) Central 2 Umezono 1–1-1 Tsukuba 305-8568 Japan

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Correlation analysis of strongly fluctuating atomic volumes, charges, and stresses in body-centered cubic refractory high-entropy alloys

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Physical Review materials 2020年第2期4卷 023608-023608页

作者： Shoji Ishibashi Yuji Ikeda Fritz Körmann Blazej Grabowski Jörg Neugebauer Computational Materials Design Max-Planck-Institut für Eisenforschung GmbH D-40237 Düsseldorf Germany Research Center for Computational Design of Advanced Functional Materials (CD-FMat) National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Ibaraki 305-8568 Japan Center for Materials Research by Information Integration (CMI2) Research and Services Division of Materials Data and Integrated System (MaDIS) National Institute for Materials Science (NIMS) Tsukuba Ibaraki 305-0047 Japan Institute of Materials Science University of Stuttgart Pfaffenwaldring 55 D-70569 Stuttgart Germany Materials Science and Engineering Delft University of Technology 2628 CD Delft The Netherlands

Local lattice distortions in a series of body-centered cubic alloys, including refractory high-entropy alloys, are investigated by means of atomic volumes, atomic charges, and atomic stresses defined by the Bader charge analysis based on first-principles calculations. Analyzing the extensive data sets, we find large distributions of these atomic properties for each element in each alloy, indicating a large impact of the varying local chemical environments. We show that these local-environment effects can be well understood and captured already by the first and the second nearest neighbor shells. Based on this insight, we employ linear regression models up to the second nearest neighbor shell to accurately predict these atomic properties. Finally, we find that the elementwise-averaged values of the atomic properties correlate linearly with the averaged valence-electron concentration of the considered alloys.

关键词： Body-centered cubic Disordered alloys Density functional theory First-principles calculations

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Gate controlling of quantum interference and direct observation of anti-resonances in single molecule charge transport (vol 18, pg 357, 2019)

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NATURE materials 2020年第1期19卷 127-127页

作者： Li, Yueqi Buerkle, Marius Li, Guangfeng Rostamian, Ali Wang, Hui Wang, Zixiao Bowler, David R. Miyazaki, Tsuyoshi Xiang, Limin Asai, Yoshihiro Zhou, Gang Tao, Nongjian Biodesign Center for Bioelectronics and Biosensors Arizona State University Tempe USA Research Center for Computational Design of Advanced Functional Materials (CD-FMat) National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Japan Laboratory of Advanced Materials State Key Laboratory of Molecular Engineering of Polymers Fudan University Shanghai China State Key Laboratory of Analytical Chemistry for Life Science School of Chemistry and Chemical Engineering Nanjing University Nanjing China London Centre for Nanotechnology and Department of Physics and Astronomy University College London London UK International Centre for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) Tsukuba Ibaraki Japan

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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Electrode potential from density functional theory calculations combined with implicit solvation theory

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Physical Review materials 2018年第9期2卷 095801-095801页

作者： Jun Haruyama Tamio Ikeshoji Minoru Otani Research Center for Computational Design of Advanced Functional Materials (CD-FMat) National Institute of Advanced Industrial Science and Technology (AIST) 1-1-1 Umezono Tsukuba Ibaraki 305-8568 Japan

We present a method that makes it possible to determine an electrode potential in an electrode/electrolyte solution system. We consider the electrode potential of the standard hydrogen electrode (SHE) reaction R:1/2H2(gas)+H2O(1MHClaq.)↔H3O+(1MHClaq.)+e− (electrode M), and conduct density functional theory (DFT) calculations combined with the effective screening medium (ESM) method and the reference interaction site model (RISM). The electrostatic field from a charged slab described by DFT with ESM is screened by that from the charge distribution in an electrolyte solution. This screening enables us to define the inner potential ΦS at the bulk solution region, which is the reference potential for the electrode potential, that is, the chemical potential of electrons (μe). Grand potentials of the left and right sides in reaction R at the equilibrium point derive the corresponding SHE potential of μeSHE=−5.27eV vs ΦS for a Pt(111) electrode. Another pathway that uses the free energy difference gives the same SHE potential; the equivalence of the electrode potentials from chemical potential and from free energy difference is validated within ESM-RISM. Even using a different electrode of Al yields the value of μeSHE=−5.22eV vs ΦS, which indicates that the electrode potential is independent of the electrodes. Finally, the potential energy profile in a vacuum/metal/solution/vacuum region shows that a difference between the inner and outer potentials is necessary to compare an absolute SHE potential and the SHE potential vs ΦS.

关键词： Electrochemical properties Interface & surface thermodynamics Surface & interfacial phenomena Liquid-solid interfaces Metals Density functional theory

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Traveling without dwelling: Extending the timescale accessible to molecular dynamics simulation

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Physical Review research 2019年第3期1卷 033032-033032页

作者： Tetsuya Morishita Atsushi M. Ito Research Center for Computational Design of Advanced Functional Materials (CD-FMat) National Institute of Advanced Industrial Science and Technology (AIST) 1-1-1 Umezono Tsukuba 305-8568 Japan Mathematics for Advanced Materials Open Innovation Laboratory (MathAM-OIL) AIST c/o AIMR Tohoku University 2-1-1 Katahira Aoba-ku Sendai 980-8577 Japan National Institute for Fusion Science 322-6 Oroshi-cho Toki 509-5292 Japan

Molecular dynamics (MD) simulations have been widely recognized as a promising tool for investigating dynamical processes with an atomic resolution. The time span accessible to MD simulations is, however, extremely limited, which makes it difficult to simulate dynamical events on a timescale of milliseconds or longer while maintaining the microscopic-level resolution. Here, we present an approach that allows us to accelerate the dynamical processes (infrequent events) by introducing an additional bias potential and to describe these events on the correct timescale. To this end, we utilize a reparametrization of time (generalized Poincaré time transformation), which leads to the accelerated dynamics and the biased sampling in phase space. The direct link between the timescale and biased sampling demonstrated in this study makes it possible to extend the timescale in MD simulations without invoking the approximation of the transition state theory. A general form of the bias potential is also introduced, which is easily constructed and straightforwardly applied to various systems. The present approach, Poincaré boost dynamics, is applied to the diffusion process of an impurity atom in an amorphous matrix and to conformational changes of a model protein for demonstrating its validity and versatility.

关键词： Chemical Physics & Physical Chemistry Amorphous materials Liquids Surfaces Molecular dynamics Multiscale modeling

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