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Computational Materials Science
Elsevier Science Publishers B.V.
Computational Materials Science

Elsevier Science Publishers B.V.

0927-0256

Computational Materials Science/Journal Computational Materials ScienceISTPSCIEI
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    A 3D orthogonal vision-based band-gap prediction using deep learning: A proof of concept

    Ponce, HiramOrtiz-Medina, JosueEspinosa, Ricardo
    8页
    查看更多>>摘要：In this work, a vision-based system for the electronic band-gap prediction of organic molecules is proposed using a multichannel 2D convolutional neural network (CNN) and a 3D CNN, applied to the recognition and classification of 2D projected images from 3D molecular structure models. The generated images are input into the CNN for an estimation of the energy gap, associated with the molecular structure. The public data set used in this research was the Organic Materials Database (OMDB-GAP1). A data transformation from the descriptive information contained in the data set to three 2D orthogonal images of molecules was done. The training set is composed of 30,000 images, whereas the testing set was composed of 7500 images, from 12,500 different molecules. The multichannel 2D CNN architecture was optimized via Bayesian optimization. Experimental results showed that the proposed CNN model obtained an acceptable mean absolute error of 0.6780 eV and root mean-squared error of 0.7673 eV, in contrast to two machine learning methods reported in the literature used for band-gap prediction based on conventional density function theory (DFT) methods. These results demonstrate the feasibility of CNN models to materials science routines using orthogonal images projections of molecules.
      原文链接:
    • NSTL
    • Elsevier

    Ab initio calculation of electron temperature dependent electron heat capacity and electron-phonon coupling factor of noble metals

    Li, YongnanJi, Pengfei
    8页
    查看更多>>摘要：Noble metal nanoparticles show fantastic catalytic property in various practical applications. It is a promising way to obtain nanoparticles from femtosecond laser ablation of noble metals. The calculation concentrates on electron heat capacity and electron-phonon coupling factor, which are two pivotal parameters describing the femtosecond laser-induced electron heating and the electron-phonon coupled energy transportation. The evolutions of these two parameters with increasing electron temperature are presented. It is found that the evolutions of the electron heat capacity and electron-phonon coupling factor are mainly affected by the electron density of states and the Fermi-Dirac distribution function.
      原文链接:
    • NSTL
    • Elsevier

    Graphene/Phosphorene nano-heterostructure as a potential anode material for (K/Na)-ion batteries: Insights from DFT and AIMD

    Mansouri, ZouhirAl-Shami, AhmedLahbabi, SalmaEl Kenz, Abdallah...
    11页
    查看更多>>摘要：Rechargeable Potassium and Sodium-ion batteries started to receive a vast amount of attention in recent years against their Lithium-ion counterparts. However, the development of a high-performing anode material for these ion batteries is still to be explored. In this work, we conduct a first-principles study on the adsorption and diffusion behaviors of Potassium (K) and Sodium (Na) in a Graphene/Phosphorene (G/P) van der Waals nanoheterostructure, in order to assess its suitability as an anode for both K-ion and Na-ion batteries. We investigate the electrochemical properties of the system, including binding energies, band structure, ion diffusivity outside and in-side the G/P system, as well as the heterostructure's stability at a high metallic coverage. The calculated binding energies for K and Na are -2.69 eV and -2.42 eV, respectively, which are strong enough to prevent metallic clustering during the cycling. The diffusion of K/Na within G/P's regions shows strong directional anisotropy with a low diffusion barrier of 0.04 eV for K and 0.05 eV for Na along the zigzag direction. We also observe that the addition of K/Na atoms into the G/P system turns its semi-metallic nature into a metallic one. Moreover, we demonstrate that the intercalation of K/Na atoms within the G/P structure give low operating potentials of approximately 0.29 V for K and 0.58 V for Na. Thus, the nano-heterostructure can provide a theoretical storage capacity of 433 mAh/g and 580 mAh/g respectively for K and Na. Finally, the thermal stability of a fully potassiated/sodiated G/P system at room temperature is revealed by the ab-initio MolecularDynamics (AIMD) calculations. Considering all these properties, we conclude that the G/P nano-heterostructure can be considered as a good candidate for negative-electrode-materials for both K- and Na-ion batteries.
      原文链接:
    • NSTL
    • Elsevier

    Structure-mechanical property relations of nanoporous two-dimensional gallium selenide

    Fang, Te-HuaDinh-Quan DoanThi-Bao-Tien Tran
    20页
    查看更多>>摘要：We apply molecular dynamics simulations to investigate the mechanical properties and atomistic deformation mechanisms of nanoporous gallium selenide (NPGS) nanosheets under uniaxial tension. The NPGS membranes structure-mechanical property correlation is investigated, especially the influences of temperature, neck width, pore shape, relative density, pore size, and strain rate. This work analyses the structural progression, initiation, fracture, brittle failure, Young's modulus, ultimate strength, fracture strain, material toughness, and critical energy release rate. In most tensile cases, crack initiates at high-stress concentration regions such as pore edges or pore corners. The crack propagates in the perpendicular with tension direction and especially prefers to spread in the zigzag directions of membranes. We also find that the increasing temperature improves the atom kinetic energy, accelerating the fracture process and significantly reducing the material mechanical properties. The relative density is a particular essential parameter to determine material mechanical properties. Likewise, the size effect of neck width indicates both material characteristics, including "smaller is tougher" and "smaller is stronger". Pore shape, notably diamond-pore, influences the stress distribution and stress absorption due to different tensile neck widths, leading to different mechanical responses, especially the material toughness. However, some material mechanical parameters were not much affected by some symmetrical pore shapes and strain rates. Remarkably, the stress distribution in the loading direction notably decreases the material mechanical performance. We also estimate the function between material mechanical properties and relative density or neck width as scaling laws to predict the mechanical properties of the NPGS nanosheets. The study results in an additional emphasis on mechanical behaviors and potentially expedites the promising applications of NPGS membranes.
      原文链接:
    • NSTL
    • Elsevier

    Orientation dependence of microstructure deformation mechanism and tensile mechanical properties of Nickel-based single crystal superalloys: A molecular dynamics simulation

    Chen, BinWu, Wen-PingChen, Ming-Xiang
    8页
    查看更多>>摘要：In this paper, molecular dynamics (MD) simulations are performed to investigate the tensile deformation mechanisms and mechanical properties of superalloys with different orientations. The research results show that the superalloys exhibit anisotropy of mechanical properties and are consistent with previous experimental research results. The anisotropy of mechanical properties is related to the differences of stability at the interfacial dislocation network and the 1/6(11 2){1 1 1} slip system startup of superalloys with different orientations. When the yield point is reached, dislocations and stacking faults on both sides of the slip plane will contact each other and merge into a stacking fault band to penetrate into the gamma' precipitates. Meanwhile, the dislocation density and the proportion of face-centered cubic (FCC) structure with different orientation models have a sudden change at the yield point. As the temperature increases, the yield strength and elastic modulus decrease in the (110) and (1 1 1) orientation models, whereas the (100) orientation model has an anomalous yield behavior. This is mainly related to the destruction of dislocation network, the change of deformation mechanism and the thermally activated cross-slip mechanism when the temperature increases.
      原文链接:
    • NSTL
    • Elsevier

    A variable-gap model for helium bubbles in nickel

    Fokt, M.Adjanor, G.Jourdan, T.
    9页
    查看更多>>摘要：In nuclear fission reactors, the amount of helium produced in materials by transmutation reactions at the end of the lifetime may reach several thousands of atomic parts per million (appm). Such high levels of helium production can impact the evolution of microstructures, particularly by forming helium bubbles. To better understand the role of helium on the stability of bubbles, a "variable-gap model"was parametrized with molecular dynamics (MD) calculations performed in nickel. This model predicts binding energies in a good agreement with MD values, especially for large bubbles. For very small bubbles, the influence of magic number sizes and faceting is more complex than can be described with the model. For these cases, it is proposed to use MD values directly.
      原文链接:
    • NSTL
    • Elsevier

    Anisotropy in interface stress at the bcc-iron solid-melt interface: Molecular dynamics and phase field crystal modelling

    Kumar, SushilLiu, Ming-WeiWu, Kuo-AnGururajan, M. P....
    10页
    查看更多>>摘要：The interface stresses at of the solid-melt interface are, in general, anisotropic. The anisotropy in the interfacial stress can be evaluated using molecular dynamics (MD) and phase field crystal (PFC) models. In this paper, we report our results on the evaluation of the anisotropy in interface stress in a bcc solid with its melt. Specifically, we study Fe using both MD and PFC models. We show that while both MD and PFC can be used for the evaluation, and the PFC and the amplitude equations based on PFC give quantitatively consistent results, the MD and PFC results are qualitatively the same but do not match quantitatively. We also find that even though the interfacial free energy is only weakly anisotropic in bcc-Fe, the interfacial stress anisotropy is strong. This strong anisotropy has implications for the equilibrium shapes, growth morphologies and other properties at nano-scale in these materials.
      原文链接:
    • NSTL
    • Elsevier

    DIMS: A tool for setting up defects and impurities CASTEP calculations

    Christopoulos, Stavros-Richard G.Papadopoulou, Konstantina A.Konios, AlexandrosParfitt, David...
    5页
    查看更多>>摘要：In the present study, we introduce a new tool for calculating the properties of different crystallographic structures, either pure or with defects. The proposed software's three different modes regarding the inputs it accepts, i.e., automatic, semi-automatic and manual, are explained. Vacancies, anti-sites, interstitials and dopants can be processed, in any number of combinations. In addition, research studies where the tool has been already applied are provided. Finally, we describe the advantages of the proposed tool regarding mass calculations, time management and human error, and we showcase, through the means of performance analysis, its weak and strong points using two case studies.
      原文链接:
    • NSTL
    • Elsevier

    Insight of displacement cascade evolution in gallium arsenide through molecular dynamics simulations

    Tian, ShangHe, HuanLiao, WenlongBai, Yurong...
    12页
    查看更多>>摘要：Displacement damage induced by space radiation is still a considerable challenge of expanding application of GaAs-based devices (e.g. solar cell, et al.) in space missions. In the current work, molecular dynamics (MD) simulations are applied to investigate displacement cascades evolution in GaAs at room temperature. A set of displacement events initiated by different energies (up to 50 keV) of primary knock-on atom (PKA) were simulated. An improved Wigner-Seitz (W-S) cell method was developed by introducing a simple criterion for more accurate identification of interstitials and antisites. Based on the present defect analysis method, the generation, evolution and distribution of point defects were discussed at first. Then, the mechanisms of both vacancy and interstitial cluster evolutions along simulation time were presented. The results indicate that both Ga and As type defects play the same crucial role among interstitials, antisites and vacancies. As the energy of PKA increases, the start points of heat spike phase postpone slightly. Moreover, the non-linear increase of surviving defects accompanied with the rise of the energy of PKA is considered as contribution of directly amorphous pockets. During the stage I of cascade, as time progresses, different size clusters show up in succession from small size (i.e., between 2 and 5) to larger size. The medium and large vacancy clusters virtually only exist in the middle of cascades, and the majority of vacancies belong to the categorizes of single vacancy and small clusters, especially at the end of cascades. However, the medium and large interstitial clusters incline to hold up or grow continually at the MD time scale once they build up. Meanwhile, interstitials in larger clusters (30 similar to) account for more fraction as the energy of particles increases.
      原文链接:
    • NSTL
    • Elsevier

    Investigation of LiMn1-xMxPO4 (M = Ni, Fe) as cathode materials for Li-ion batteries using density functional theory

    Hasnaoui, A.Oukahou, S.Elomrani, A.Maymoun, M....
    11页
    查看更多>>摘要：Olivine LiMnPO4 (LMP) is attracted significant attention as cathode material for lithium ion batteries (LIBs), due to its high voltage and capacity. However, LMP suffers from low electronic and ionic conductivities, therefore in this current work we have focused to overcome these drawbacks by substitutions the Mn sites in LMP by different concentrations of Ni and Fe. That is, LiMn1-xMxPO4 (M = Ni, Fe; x = 0, 0.25, 0.5, 0.75, 1). The structural, electronic, electrochemical potential and magnetic properties of lithiated/delithiated (LiMn1-xMxPO4/Mn1xMxPO4 (M = Ni, Fe; x = 0, 0.25, 0.5, 0.75, 1)) phases were investigated beside kinetic properties and capacity storage of Li-ion. The results reveal that Ni and Fe affected the structural, electronic, kinetic, electrochemical potential and magnetic properties. The unit cell volume of LMP were decreased with increasing Ni and Fe concentrations in Mn sites, this behavior could be explained by the difference in ionic radius of doping cations Mn2+, Ni2+ and Fe2+. The open circuit voltage of LiMn1-xNixPO4 was slightly increased from 4.39 V (for LMP) to 4.41 V (for LiMn0.25Ni0.75PO4) which indicate a good improvement of Li-intercalation voltages with increasing the concentration of Ni. Moreover, band gap (Eg) of LMP (3.62 eV) is reduced with substitutions of Mn sites by Ni and Fe especially for the compounds LiMn0.5Ni0.5PO4 (2.77 eV) and LiMn0.5Fe0.5PO4 (3.35 eV) and improve the electronic conductivity. Moreover, the diffusion energy barrier of Li-ion in Mn0.5Ni0.5PO4 (0.34 eV) and Mn0.5Fe0.5PO4 (0.39 eV) were lower than pristine MnPO4 (0.42 eV), indicates that 50 % of Fe and Ni are beneficial to improve the kinetic properties in LMP. This study suggest that LiMn0.5Ni0.5PO4 (LMNP) and LiMn0.5Fe0.5PO4 (LMFP) are great alternatives of LMP for cathode materials in LIBs due to their high performance compared to the pristine LMP.
      原文链接:
    • NSTL
    • Elsevier