查看更多>>摘要：Intrinsic defects and hydrogen play an essential role in regulating photocatalytic properties of semiconductor materials. Bismuth oxychloride (BiOCl) is an important ternary bismuth-based photocatalytic material, for its wide bandgap allows band-gap engineering to tailor its properties. In this paper, we use first-principles to study the effects of intrinsic defects and hydrogen on the electronic structure of BiOCl. We studied the intrinsic defect formation energies, defect electronic structures and the diffusion of these defects in BiOCl. We found that the ptype conductivity and band gap variation in BiOCl may be caused by the Fermi level pinning effect and intrinsic defective states around the band edges. Intrinsic defects of Hint, OCl and BiCl show delocalized features which may have a predominant effect for carrier transfer. As the temperature rises, the diffusion of oxygen vacancies in the xy plane goes up most drastically, while the diffusion of interstitial hydrogen in the yz plane changes smoothest and has the fastest speed. Our work offers fundamental insights for explaining the band gap variation, p-type conductivity and the transport of defects in BiOCl and provides basic guidance in regulating the photocatalytic performance of BiOX (X = Cl; Br; I) by defect engineering.
查看更多>>摘要：A multiscale approach is presented to calculate the hydrogen diffusion in amorphous In-Ga-Zn-O (a-IGZO). Based on the fact that the presence of oxygen vacancy (VO) defects suppresses the hydrogen diffusion in a-IGZO, the simulated H diffusion depth is utilized to evaluate the VO concentration (nVo). The kinetic Monte Carlo (kMC) simulation is carried out to obtain the depth profiles of H diffusion in a-IGZO, which uses input of the H migration energy barriers (EA) calculated within the density functional theory (DFT) method. The DFT calculations showed that when H occupies the VO defects, its EA becomes higher than that of the interstitial H, which eventually suppresses H diffusion. The H diffusion function depending on nVo and temperature, fD(nVo,T), is readily obtained fitting the complementary error function to the simulated H diffusion profile. It is observed that fD(nVo,T) can closely reproduce the experimentally measured H diffusion from literature with nVo being comparable to the measured carrier concentration that can be speculated as the upper limit of nVo. The properties of H diffusion in a-IGZO are examined in detail to address the application of the presented approach for estimation of nVo.
查看更多>>摘要：The recent growth in data volumes produced by modern electron microscopes requires rapid, scalable, and flexible approaches to image segmentation and analysis. Few-shot machine learning, which can richly classify images from a handful of user-provided examples, is a promising route to high-throughput analysis. However, current command-line implementations of such approaches can be slow and unintuitive to use, lacking the real-time feedback necessary to perform effective classification. Here we report on the development of a Python-based graphical user interface that enables end users to easily conduct and visualize the output of few-shot learning models. This interface is lightweight and can be hosted locally or on the web, providing the opportunity to reproducibly conduct, share, and crowd-source few-shot analyses.
查看更多>>摘要：To simulate the photoexcited molecular dynamics of strongly correlated materials, we implement the Hubbard U term for the proper account of the on-site Coulomb interaction in the real-time time dependent density functional theory (TDDFT + U) molecular dynamics simulations. As a prototype example, we present first-principles simulations of excited state dynamics in a typical transition metal oxide (rutile TiO2) containing d-orbital electrons. We find an unphysical divergence originated from the overcoherence in the evolution of density matrix, which can be alleviated by a diagonalization procedure proposed here. Upon this correction, we identify an intrinsic charge localization dynamics in rutile TiO2 upon photoexcitation, which offers a microscopic understanding of the photoinduced processes in correlated transition metal oxides.
查看更多>>摘要：We studied the shape stability of Pt3M alloy nanoparticles (NPs) using density functional theory calculations, where M is Co or Ni. The relationship between the shape and durability of Pt3M NPs is reported. We evaluated the cohesive energies of face-centered cubic (fcc) and face-centered tetragonal (fct) NPs. Truncated octahedron, icosahedron, and truncated cube were considered as shapes for the fcc NPs. The cohesive energies in the truncated octahedral fcc Pt NPs were lower than other shapes, while the icosahedral fcc and truncated octahedral fct Pt3M NPs with the Pt-skin configuration were stable. Co and Ni had lower twin boundary energies than Pt, thus affecting the stability of the icosahedral fcc Pt3M NP; another factor influencing the stability was the high coordination number. An increase in Pt-M bond fraction lowered the cohesive energy of truncated octahedral fct Pt3M NPs. The expansion of the icosahedral fcc NPs competed with the shrinking effect of alloying, thus affecting the d-band center in icosahedral fcc Pt3M NPs. Due to the suppression of the charge transfer and shrinkage effect by alloying, d-band center in the facet with coordination number = 9 was adjusted to the suitable range based on the volcano plot.
查看更多>>摘要：This paper addresses the descriptors-based characterization of dense 3D microstructures using the unifying concept of accessibility, mixing local shape features with global topology. Underlying percolation and constrictivity features are jointly considered by probing the connected components of the microstructure with structuring elements with increasing sizes. Adapted morphological operations are combined to provide a scalable protocol embedding suitable descriptors applied on accessible volumes, yielding a sharp discrimination power. The suggested framework named A-protocol can efficiently analyze complex microstructures by applying a stratified sampling for the selection of paths' endpoints, when connected. It stops when percolation ends, at a critical radius value. The A-protocol is tested on Cox multi-scale Boolean models using the Euler number as an arbitrarily chosen embedded descriptor. This computational protocol is available in the open access software environment plug im!.
查看更多>>摘要：The microstructural evolution of 4.5 nm grain-sized nanocrystalline aluminum under high pressure shear loading is investigated using molecular dynamics simulations. A compression of 15 GPa is applied to the system concurrently with a shear deformation rate of 3.21 x 10(9) s(-1). Results show that the microstructural evolution is marked by a transient grain refinement regime followed by a steady grain growth process within 1 ns, coarsening the microstructure from 4.5 nm to 5.8 nm average grain size. The grain growth process is mediated by three independent deformation mechanisms: i) grain rotation; ii) grain boundary sliding; iii) and grain boundary migration. While the first two mechanisms are inherent grain boundary deformation mechanisms, the latter is driven by intense dislocation activity. Data indicates that during the deformation the dislocation density surges from 5 to 15 x 10(11) cm(-2) , highlighting the important role of dislocation dynamics in the evolution of the microstructure. These atomistic insights shed light on the underlying complex incipient deformation processes, which are activated during severe plastic deformation of nanocrystalline materials.
查看更多>>摘要：An interatomic potential (termed EAM-21) has been developed with the embedded atomic method (EAM) for CrFeMnNi quaternary HEAs. This potential is based on a previously developed potential for CrFeNi ternary alloys. The parameters to develop the potential were determined by fitting to experimental values, density functional theory (DFT) and thermodynamic calculations, to reproduce the main crystal characteristics, namely: the stability of the fcc phase, elastic constants, and stacking fault energy. Its applicability for the study of plastic deformation mechanisms was checked by calculations of behaviour of a 1/2 < 1 1 0 >{1 1 1} edge dislocation in equiatomic quaternary CrFeMnNi alloy, as well as its less-complex subsystems (ternaries, binaries, and pure metals). The calculations were performed in the domain of temperatures between 0 and 900 K; smooth and stable glide of an edge dislocation and fcc phase stability in this temperature range was confirmed. This study demonstrates the suitability of the EAM-21 potential for the analysis of plasticity mechanisms and mechanical properties of CrFeMnNi HEAs.
查看更多>>摘要：Hydrogen impurities in metal oxides are targets of experimental and theoretical investigations because of their crucial influences on material properties. However, systematic modeling of the hydrogen impurities is not straightforward as they show a large variety of configurations depending on the host oxides, especially at interstitial sites. In this study, we utilize the electrostatic potential, electron localization function, and charge density for recommending interstitial hydrogen positions in metal oxides. We consider (i) local minima of the electrostatic potential and (ii) local maxima of the electron localization function as interstitial proton sites, and (iii) local minima of the charge density as interstitial hydrogen-atom and hydride-ion sites. We assess the validity of these recommendations using first-principles calculations for hydrogen impurities in 20 common metal oxides and show that the combination of definitions (i)-(iii) is capable of efficiently finding the most stable interstitial configurations, especially for protons and hydride ions. The present approach can substantially narrow the search space for interstitial hydrogen positions, thereby reducing the overall computational costs for modeling hydrogen impurities.
查看更多>>摘要：Porous metal structures produced by electrochemical dealloying have been extensively studied for use in various applications that require high surface areas. A new comprehensive multi-phase-field (MPF) model is proposed to study topological porous patterns formed by spontaneously etching a bulk binary alloy that involves electrochemical reactions, bulk and surface diffusion, ion transport, applied electrode potential, and charge conservation. The governing equations for the alloy-porous cluster-electrolyte system account for a generalized ButlerVolmer electrochemical reaction and are in accordance with the classical nucleation theory. Based on a quantitative examination of the effects of electrode potential and precursor composition, the simulation results reproduce typical phenomena including passive surface dealloying, active porosity evolution, critical potential, and characteristic length scale in two-dimension (2-D) and three-dimension (3-D). To consider more complicated dealloying systems, the evolutions of a bimodal porous metal structure, nanocomposite, and nested porous network with a structured hierarchy are investigated. The proposed model can be a useful tool for understanding and predicting the morphology evolution of diverse porous structures during electrochemical dealloying.
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Elsevier