查看更多>>摘要：Due to the complexity of scaling mechanism, conclusions obtained from different experiments could be controversial. To reveal the scaling mechanism at the molecular level, this work studies the effect of temperature, ion concentration, and substrate material on CaCO3 scaling via molecular simulation. Molecular dynamics (MD) calculations show that CaCO3 tends to form above a specific critical temperature in different systems. Affected by the interaction of scaling ions and clusters, the scaling ability of Fe(1 1 1) first increases and then decreases with increasing concentration. Moreover, the results of MD and density functional theory (DFT) show that the scaling capacity of Fe(1 1 1), Ni(1 1 1), and Cu(1 1 1) decreases successively. This work would throw light on studying scaling mechanism in complex environment.
查看更多>>摘要：Diamond-like carbon (DLC) films possess excellent tribological properties, such as low friction and high wear resistance. However, DLC films detach easily owing to the high residual stress, which limits their application on mechanical sliding surfaces. To overcome this problem, it is crucial to clarify the residual stress generation mechanism in DLC films. In this study, molecular dynamics simulations were conducted on the deposition process of a DLC film to clarify the residual stress generation mechanism. The results suggest that sp(3) hybridization clusters are nucleated in the sp(2) formed on the film surface, and sp(3) clusters grow in the sp(2 )carbon through the sp2 -> sp(3 )bond change during the film growth process. The bond length of sp(3) was approximately 8.5% larger than that of sp(2) under stress-free bulk conditions. Thus, when the sp2 -> sp3 bond change occurs under construction by surrounding atoms, compressive stress is generated in the sp(3) cluster, which increases with the growth of the sp(3) cluster. Based on the results, we conclude that the nucleation and growth of sp(3) clusters in sp(2) result in residual compressive stress in the DLC film. We believe that the present mechanism clarification of the stress development process in DLC films will facilitate the development of new methods for residual stress reduction.
查看更多>>摘要：The ligand on the surface is an important factor for the improvement of the CO2 adsorption capacity of a metal-organic framework (MOF). In this work, the hydroxyl and carboxyl functional groups that have different attractions to water molecules are connected separately to the metal-organic framework, Mg-MOF-74, and their effect on humid CO2 adsorption capacity is investigated using molecular dynamics simulations. The humid CO(2 )adsorption capacity of Mg-MOF-74, Mg-MOF-74-OH, and Mg-MOF-74-COOH present linear proportional re-lationships to the volumetric concentration of CO2. It is found Mg-MOF-74-COOH has the best CO2 adsorption capacity from the mixture gas with high humidity. Owing to the competitive adsorption of H2O and CO2 at the open sites, the more sensitive to H2O the MOFs are, the less they absorb CO2. Hence, Mg-MOF-74-COOH is mostly favorable for adsorbing CO2, followed by Mg-MOF-74 and Mg-MOF-74-OH. Meanwhile, the difference in adsorption heat between H2O and CO2 is over 3 times for Mg-MOF-74-OH; and it becomes about 1.5 times for Mg-MOF-74, while it is negligible for MOF-74-COOH. The results show that by synthesizing a MOF with high CO2 selective adsorption and low sensitivity to impurities, especially water molecules, it can be widely used in inustrial applications, thus this work has a guiding significance for developing and synthesizing new materials by ligand functionalization of high surface area MOFs which are promising in carbon capture technology.
查看更多>>摘要：Pseudo-binary III-V semiconductor alloys are promising for applications in optical, photovoltaic and photo electrochemical fields, for their tunable band gaps and band alignments. In this work, we carefully investigate structural and photovoltaic properties of indium gallium phosphide (InxGa1-xP; 0 < x < 1) alloys. Using evolutionary algorithm crystal structure prediction, we perform structure searches for indentifying potential crystal structures of InxGa1-xP alloys in nine chemical compositions at zero temperature and ambient pressure. We find that InxGa1-xP alloys can adopt zinc blende (ZB) and wurtzite (WT) structures and the former generally have lower energy than the latter at all compositions. Based on these predicted InxGa1-xP structures, we evaluated their spectroscopic limited maximum efficiencies (SLMEs) and find that InxGa1-xP alloys with high In concentrations (x & GE; 0.5) have higher SLME values than those of InxGa1-xP alloys with low In concentrations (x < 0.5). We also find that SLMEs of disordered InxGa1-xP alloys are larger than those of ordered alloys due to the enhanced oscillator strengths.
查看更多>>摘要：Assembling near-infrared emitting materials with another semiconductor material is a promising approach to improve the performance of NIR light-emitting devices. Here we performed a computational and theoretical study on feasibility of improving performance PbS based near-infrared emitting devices by perovskite CsPbBr3 decorating. Physical mechanism of improved light-emitting efficiency is revealed by electronic structure calculations. The type-I band alignment of CsPbBr3/PbS interface facilitates the transferring of electrons and holes in CsPbBr3 quantum dots to PbS active material, which is confirmed by the charge density difference results. The rather small lattice mismatch and analogous octahedral framework ensure an almost perfect contact and little density of gap states at CsPbBr3/PbS interface. The improved light absorption in CsPbBr3/PbS heterostructured nanocrystals ensures an enhanced near-infrared light-emitting in PbS. Our work provides a theoretical understanding on the physical mechanism of improved near-infrared emitting performance in CsPbBr3 decorated PbS based light-emitting devices, and suggests a promising route to design near-infrared emitting devices with high performance.
查看更多>>摘要：3d-5d double perovskite is one kind of the most promising materials due to its novel properties and excellent performance with strong spin-orbit coupling. We used machine learning (ML) to search new 3d-5d perovskites. Three new methods derived from rescaling strategy in training models are used to solve the imbalanced problem which is more effective and more accurate than conventional machine learning models. Out of 664 scanned candidates of A(2)BB'O-6 double perovskite (A is nonmagnetic metal, B and B' are 3d and 5d transition metals, respectively), we find 166 compounds can be stable 3d-5d double-perovskite structures, where A cations have to be +3 or +2 changed. Our results may throw light on the development of perovskite-based devices with strong spin-orbital couplings.
查看更多>>摘要：Rutile TiO2 with intrinsic defects or doped by specific elements will emerge excellent electromagnetic property and optical characteristics, such as room temperature ferromagnetism. In this study, we studied the effects of intrinsic defects and Co atoms on the electromagnetic structures and optical properties of rutile TiO2 by Density Functional Theory. The results show that the magnetic moment is produced by intrinsic defects such as V-O and Ti-i while the Co atom can also polarize the system. The magnetism of Co doped TiO2 does not come entirely from Co atom. There will be a change in charge population when O and Ti are close to Co atoms, which will produce local spin magnetic moment. The hybridization of Co:3d, Ti:3d and O:2p orbitals leads to the generation of new impurity levels in the band gap, which reduces the E-g of rutile TiO2 and improves the visible light absorption, resulting in the red-shift of the light absorption edge of Co doped TiO2. In addition, the optical properties of both pure rutile TiO2 and Co doped TiO2 are anisotropic, especially along [001] direction.
查看更多>>摘要：In this article, non-equilibrium molecular dynamics-based simulations were performed to study the effect of shock compression on the deformation governing mechanism of high entropy alloys (HEA). Quinary configuration of the alloy containing (Co-Cr-Cu-Fe-Ni) as primary elements were considered, and interaction between them was simulated with the help of embedded atom method potential. Hugoniot curves between P-Up and Us-Up were captured for HEA that agrees qualitatively and quantitatively with results reported using higher fidelity simulations and experimental techniques. Single-crystal HEA was subjected to shock compression and ultra-short pulse at piston velocities above and below the Hugoniot elastic limit. To capture the dynamics of the shock wave propagation in single-crystal HEA, spectra-temporal distribution of pressure and velocities were captured as a function of time from the onset of the shock wave. It was predicted from atomistic simulations that the insertion of voids in the path of shock front helps in dispersing the energy, as well as reducing the speed of shock propagation. Voids significantly affect the shock deformation governing mechanism in the crystal of HEA, and onset plastic deformation, even at piston velocities below the Hugoniot elastic limit. To capture the effect of lattice distortion in HEA, average atom configuration was also developed. It was predicted from the simulations that the effect of lattice distortion helps in blunting the shock front and diluting its speed of propagation. The lattice distortion effect is more dominant at lower simulation temperatures and lower piston impact velocities.
查看更多>>摘要：The growth or dissolution of a particle under compression or simple shear is investigated by means of an analytical approach. The changes in shape and size of the particle are determined by the combination of two interphase movements: migration (with respect to matter) and advection (driven by the moving matter). The problem is solved by an indirect original method, where the particle surface is derived as the envelope of a family of straight lines (2D) or planes (3D), which leads to closed form parametric equations. It is shown that the shapes of deformed particles are close to, and can be fitted by, ellipsoids. The equivalent strain dependence of the aspect ratio is similar for both investigated loading paths: particle flattening or elongation is reduced by growth, and conversely increased during dissolution. Finally, upon growth from a zero initial radius, the aspect ratio is a function of the applied strain only, which is contrary to intuition.
Elahi, S. M.Tavakoli, R.Boukellal, A. K.Isensee, T....
13页
查看更多>>摘要：We present a computational framework for the simulations of powder-bed fusion of metallic alloys, which combines: (1) CalPhaD calculations of temperature-dependent alloy properties and phase diagrams, (2) macroscale finite element (FE) thermal simulations of the material addition and fusion, and (3) microscopic phase-field (PF) simulations of solidification in the melt pool. The methodology is applied to simulate the selective laser melting (SLM) of an Inconel 718 alloy using realistic processing parameters. We discuss the effect of temperature-dependent properties and the importance of accounting for different properties between the powder bed and the dense material in the macroscale thermal simulations. Using a two-dimensional longitudinal slice of the thermal field calculated via FE simulations, we perform an appropriately-converged PF solidification simulation at the scale of the entire melt pool, resulting in a calculation with over one billion grid points, yet performed on a single cluster node with eight graphics processing units (GPUs). These microscale simulations provide new insight into the grain texture selection via polycrystalline growth competition under realistic SLM conditions, with a level of detail down to individual dendrites.
NSTL
Elsevier