查看更多>>摘要：Bimetallic nanoparticles containing platinum and another d-metal are highly perspective catalysts with stability and activity superior to a single-metal platinum materials. It is known that the improvement of catalytic properties depends both from the composition and from the structural arrangement of atoms in bimetallic nanoparticles. This leads to importance of the experimental determination of the nanoparticles architecture (random solid solution, Janus, core-shell or "gradient'') for the search of novel bimetallic systems. We considered the platinum-copper nanoparticles synthesized by simultaneous or multistage sequential depositions of metals. The insight of the architecture of bimetallic PtCu nanoparticles was obtained by the study of radial distribution functions (RDFs) of metal atoms. The RDFs were obtained both theoretically, using molecular dynamics simulations, and experimentally, from the analysis of the extended X-ray absorption fine structure (EXAFS) spectra at Pt L-3- and Cu K-edges. Machine learning (ML) algorithms revealed the outstanding sensitivity of the theoretical RDFs to the architecture of the bimetallic nanoparticles: the correct architecture can be determined with 99 % confidence in terms of F1 score. The application of the variety of ML classification methods to the experimental RDFs showed the benefit K-Neighbors classification method.
Krajewski, Adam M.Siegel, Jonathan W.Xu, JinchaoLiu, Zi-Kui...
19页
查看更多>>摘要：In the present paper, we introduce a new neural network-based tool for the prediction of formation energies of atomic structures based on elemental and structural features of Voronoi-tessellated materials. We provide a concise overview of the connection between the machine learning and the true material-property relationship, how to improve the generalization accuracy by reducing overfitting, how new data can be incorporated into the model to tune it to a specific material system, and preliminary results on using models to preform local structure relaxations. The present work resulted in three final models optimized for (1) highest test accuracy on the Open Quantum Materials Database (OQMD), (2) performance in the discovery of new materials, and (3) performance at a low computational cost. On a test set of 21,800 compounds randomly selected from OQMD, they achieve a mean absolute error (MAE) of 28, 40, and 42 meV/atom, respectively. The second model provides better predictions in a test case of interest not present in the OQMD, while the third reduces the computational cost by a factor of 8. We collect our results in a new open-source tool called SIPFENN (Structure-Informed Prediction of Formation Energy using Neural Networks). SIPFENN not only improves the accuracy beyond existing models but also ships in a ready-to-use form with pre-trained neural networks and a GUI interface. By virtue of this, it can be included in DFT calculations routines at nearly no cost.
查看更多>>摘要：To improve the reliability of BCC iron-based steels in supercritical water, it is crucial to understand the atomic-scale deterioration mechanisms under stress coupled with chemical reactions at the iron/water interface. Mo-lecular dynamics simulations with the reactive force field were employed to examine the atomic-scale deterio-ration mechanisms of BCC-iron and the role of chemical reactions with supercritical water. The simulation results revealed a lower yield stress and strain for BCC-iron in supercritical water than in vacuum. Yielding of the BCC-iron in both the vacuum and supercritical water occurred through the generation of partial dislocations at the surface. The deterioration of iron in supercritical water was found to originate from chemical reactions between the iron surface and water molecules; specifically, the formation of Fe-OH bonds on the iron surface due to the dissociative adsorption of water induces displacement of the surface iron atoms, accelerating the generation of partial dislocations.
查看更多>>摘要：Reactive Molecular Dynamics simulations were run on three epoxy-amine thermoset systems, with different hardener monomer functionalities. From the obtained reference data, the degree dependence of the monomer reactivity was obtained as a function of the conversion of functional groups. Monomer reactivities were calculated and used to parametrise a polymer model including the First Shell Substitution Effect (FSSE). The model is used to run numerical simulations on a graph. Results are compared to results from graph simulations using the independent functional groups model (ideal polymerisation), and from the benchmark Molecular Dynamics simulations. With the parametrised FSSE model, it is possible to give more accurate predictions of the relevant properties of the polymer, such as the gel point.
查看更多>>摘要：With 12.7% power conversion efficiency and sustainable constituents, Cu2ZnSn(S1-x)4 (CZTSSe) is a next-generation photovoltaic front-runner. Going beyond requires maximizing two limiting parameters: open-circuit voltage and short-circuit current density. Doing so primarily necessitates synthesizing the single-phase of CZTSSe with minimal detrimental defects such as Cu-Zn and Sn-Zn antisite pairs (CuZn + SnZn, 2CuZn + SnZn) and S-vacancy (VS). Providing a framework that allows one to understand the thermodynamic limits on the single-phase stability and defect formation from the first-principles calculations, we determine that at least one anion-poor growth condition is needed to obtain the single-phase CZTSSe. Se-poor growth condition is found to be the optimal choice to this end, and Se-rich (Se/(S+Se) > 0.5) alloy composition is likely to maximize the CZTSSe's solar-to-current efficiency.
Dziegielewski, PrzemyslawEvangelakis, GeorgosAntonowicz, Jerzy
8页
查看更多>>摘要：Metallic glasses are amorphous solids, usually alloys, with liquid-like atomic structure involving short-range order characterized by clusters of atoms and medium-range order - a spatial arrangement of those clusters. Amorphous metals lack the translational symmetry of crystals, yet their atomic packing density is nearly as high as in crystalline materials. The packing density of metallic glasses can be further enhanced by external pressure, which forces the disordered structure to accommodate the load. In this work, we employ molecular dynamics simulations to follow variations of short-to-medium-range order of three binary Zr-Cu metallic glasses during hydrostatic compression from 0 to 100 GPa. Our study confirms the previously reported unusual contraction of Zr-Zr pairs. We suggest that the effect is related to the theoretically predicted step change of the electronic configuration of Zr atoms under compression. A common feature of the investigated systems is an increasing contribution of icosahedral order around Cu atoms which is accomplished by preferential straining of the mechanically soft Zr-Zr bonds. Our results reveal structural similarities of different alloys in the high-pressure regime and show that their topological short-to-medium-range order becomes composition-independent under compression. We conclude that the topology of short-to-medium-range order in Zr-Cu MGs under compression exhibits a universal, composition-independent character.
查看更多>>摘要：The influence of the grain orientation on the long-range internal stress associated with the accumulation of geometrically necessary dislocations (GNDs) during plastic deformation is numerically investigated. GNDs stored at grain boundaries (GBs) do not systematically generate a backstress inside grains. Surprisingly, longrange anti-backstress promoting dislocation dynamics and plastic strain inside grains arises at certain GBs interfaces from the accumulation of GNDs. This discovery on one important elementary mechanism affecting the macroscopic mechanical behavior of polycrystals provides guidelines to improve the physical content of current crystal plasticity models.
查看更多>>摘要：The lattice parameters, bond lengths, bond angles (octahedra tilt angles), Goldschmidt tolerance factor, density of states and electronic band structure of rare-earth scandates LnScO(3) (Ln = Eu, La, Nd, Pr, Sm and Tb) in orthorhombic structure have been investigated in the generalized gradient approximation (GGA) + U method with the on-site Coulomb interaction parameter U-eff varying from 1 to 10 eV. The lattice constants, octahedra tilt angles (except for (Eu,Tb)ScO3 compounds), mean Sc-O and Ln-O bond lengths increased almost linearly with effective U parameter values. However, the tolerance factor has decreased (except for (Eu,Tb)ScO3 compounds). Density of states and electronic band structure computations show that LnScO(3 )compounds are insulator materials and have direct electronic band gap. The electronic band gap of the compounds first increases and then decreases with increasing U-eff . (GGA) + U calculation shows a strong hybridization between Sc-3d and O-2p states. Rare-earth (Ln)-5d states contribute somewhat to this hybridization. The electronic charge distribution and (P)DOS calculation results show that the bonding behavior of LnScO(3) compound is a combination of covalent and ionic nature. Our results show that the structural and electronic properties are affected by the application of the Hubbard U term in GGA calculations and the computed lattice constants, bond distances and octahedra tilt angles deviate more from the experimental values. On the other hand, it was observed that the electronic band gap approached the experimental values at the optimal U-eff values determined for the compounds.
查看更多>>摘要：In this study, the formation and growth of intermetallic compounds (IMC) at Sn/Cu interface were studied by using the molecular dynamics method of modified embedded atom method (MEAM) potential combined with practical experiments. The formation and growth process models of IMC layer at the initial stage of soldering were improved, and the growth trend and mechanism of IMC layer were analyzed. Further analysis of diffusivity shows that the diffusivity changes exponentially during welding and is related to the nucleation and growth of intermetallic compounds. Thus, this study provides valuable insights for the subsequent study on the initial stage of Sn/Cu interface and Sn/Cu solder joint reliability.
NSTL
Elsevier