Ferguson, Joseph C.Borner, ArnaudPanerai, FrancescoClose, Sigrid...
13页
查看更多>>摘要：The diffusive tortuosity factor of a porous media quantifies the material's resistance to diffusion, an important component of modeling flows in porous structures at the macroscale. Advances in X-ray micro-computed tomography (mu-CT) imaging provide the geometry of the material at the microscale (microstructure) thus enabling direct numerical simulation (DNS) of transport at the microscale. The data from these DNS are then used to close material's macroscale transport models, which rely on effective material properties. In this work, we present numerical methods suitable for large scale simulations of diffusive transport through complex microstructures for the full range of Knudsen regimes. These numerical methods include a finite-volume method for continuum conditions, a random walk method for all regimes from continuum to rarefied, and the direct simulation Monte Carlo method. We show that for particle methods, the surface representation significantly affects the accuracy of the simulation for high Knudsen numbers, but not for continuum conditions. We discuss the upscaling of pore-resolved simulations to single species and multi-species volume-averaged models. Finally, diffusive tortuosities of a fibrous material are computed by applying the discussed numerical methods to 3D images of the actual microstructure obtained from X-ray computed micro-tomography.
查看更多>>摘要：A thermal-mechanical coupling model describing energy dissipation of cyclotetramethylene-tetranitramine (HMX) explosive particles subjected to drop-weight impact is developed based on the discrete element method (DEM). The energy dissipation resulting from plastic deformation, sliding friction and rolling friction due to the interaction of HMX explosive particles can be effectively captured during the impact loading process by DEM. The simulation results illustrate that the energy dissipation increases with the increase of drop-weight height, particle size, and moment of inertia of particle, but the energy dissipation decreases when the sample mass increases from 40 mg to 55 mg at the same impact loading condition. Moreover, it is found that the energy dissipation is dominated by interparticle friction dissipation in the absence of internal defects such as cracks or pores, which is in agreement with previously published results. Furthermore, this work reveals that the main contribution of friction dissipation is derived from rolling friction dissipation.
查看更多>>摘要：Molecular dynamics simulations were performed to investigate the performance of functionalized graphenylene membranes for seawater desalination in terms of water permeability and salt rejection. For this purpose, the functionalized graphenylene nanosheet was inserted in the simulation cell containing sodium and chloride ions. Then, molecular simulations were done for four different membrane-based systems (P1, P2, P3, and P4) under different external pressures to obtain the water permeability and salt rejection of all systems. The results demonstrated that system P1 owning fluorinated pore, shows the best performance among all systems with permeability of 11,032 L.m(-2).h(-1).bar(-1) and 99.4% salt rejection at P = 10 MPa. Also, system P3 with combined functional fluorine and hydroxyl groups at the pore, revealed the permeability of 9293 L.m(-2).h(-1).bar(-1) and 100% salt rejection at P = 5 MPa. Therefore, the hydrophilic chemical functions improve the desalination performance of membrane, which can be considered in design of water desalination systems.
查看更多>>摘要：Using first-principles calculations, we found several energetically stable structures of monolayer SnP3, which include metal (M-SnP3) and semiconductor (S-SnP3). The structural difference between M-SnP3 and S-SnP3 lies in the buckling angle, which is the reason for the metal-semiconductor transition of SnP3 from bulk to monolayer. When the biaxial strain is applied from -5% to 5%, the buckling decreases and the bond angle increases, leading to the weakened (enhanced) hybridization of the p(z)(p(x)) orbital and the increase (decrease) of the energy of the corresponding bonding state. Although the biaxial strain of 6% or - 6% does not change the structure of monolayer SnP3 from S-SnP3 to M-SnP3, a large enough compressive strain will close the band gap of semiconductor SnP3. The uniaxial tensile strain has the same effects, but exhibits anisotropic behaviors on the band near the Fermi level. There are similar situations for GeP3 and GeSnP6, which have the same valence electrons. By the investigation of structural characteristics and atomic orbital compositions, this work reveals the mechanism of strain-tuned band structures and metal-semiconductor properties, which is useful for band engineering of two-dimensional materials.
Zheng, HaoyanLiang, PeiLevin, Alexander A.Brunkov, Pavel N....
8页
查看更多>>摘要：Among all inorganic perovskite, CsPbI3 has the closest ideal bang gap for solar cells. However, the instability of metal halides hinders its commercial application. The doping of A-site organic cations might improve the stability of perovskite and also make the bandgap adjustable, thus enhance its photoelectric properties. In this paper, the structure stability, electronic structure and optical properties of CsPbI3 with five different organic cations (H3NNH2+, CH3NH3+, C3H6NH2+, CH3NH2CH3+, CH3CH2NH3+) partially alternative doping instead the A site cation have been studied by using the first principles within density functional theory. In order to get accurate description of the bandstructure information, different exchange-correlation functions, e. g. PBE, PBE + SOC and HSE were used to describe the calculated systems, our calculation results indicated that the PBE exchange-correlation function can describe the electronic properties of the systems very well in this paper. Formation energy calculation indicates that all the doping systems are thermally stable; and all the doped CsPbI3 show good tolerance factor according Goldschmidt rule. Among the five different doping systems, the bandgap of doped H3NNH2+ will decrease to 1.28 eV, while the bandstructure of other doped cations will widen the bandgap. The maximum bandgap increased to 1.65 eV with doping C3H6NH2+. However, all the band structures are mainly contributed by inorganic framework. The results suggest that the structure doped organic cations can be exited stably, and the band edge of the optical absorption spectrum will be redshifted. These properties can provide research ideas for the subsequent research of A-site doping organic cations.
查看更多>>摘要：To enable accurate molecular dynamics simulations of iron-chromium alloys with surfaces, we develop, based on density-functional-theory (DFT) calculations, a new interatomic Fe-Cr potential in the Tersoff formalism. Contrary to previous potential models, which have been designed for bulk Fe-Cr, we extend our potential fitting database to include not only conventional bulk properties but also surface-segregation energies of Cr in bcc Fe. In terms of reproducing our DFT results for the bulk properties, the new potential is found to be superior to the previously developed Tersoff potential and competitive with the concentration-dependent and two-band embedded-atom-method potentials. For Cr segregation toward the (100) surface of an Fe-Cr alloy, only the new potential agrees with our DFT calculations in predicting preferential segregation of Cr to the topmost surface layer, instead of the second layer preferred by the other potentials. We expect this rectification to foster future research, e.g., on the mechanisms of corrosion resistance of stainless steels at the atomic level.
查看更多>>摘要：In this study, structural and electronic properties of two-dimensional hybrid ZnO/graphene (ZnO/G) and ZnO/ graphene/graphene (ZnO/G/G) nanocomposites are investigated based on first-principles calculations. The calculation indicates that interlayers of the two nanocomposites exist typical van der Waals (vdW) weak interactions. The intrinsic electronic properties of ZnO and graphene monolayer are well-conserved, and the deposition on ZnO substrate opens a band gap of graphene at the Dirac point. When electric fields are applied, the ZnO/G nanocomposites exhibits semiconducting to metallic transition. The transition between Schottky and Ohmic contacts can be effectively implemented, accompanied by the conversion of p-type and n-type Schottky. Meanwhile, the projected density of states and work function of ZnO/G are deeply investigated to discuss the effects of orbital and charge transfer. Compared to ZnO/G, ZnO/G/G would overcome the lower Schottky barrier height (SBH) to form Ohmic contacts, indicating a higher sensitivity to electric field modulation. The formation of low-resistance Ohmic contact has important application for high-performance semiconductor devices.
查看更多>>摘要：We performed a first-principles study of the electronic behavior of a 2D hexagonal boron phosphide monolayer (2D-h-BP). The system was deformed isotropically by applying a simultaneous tensile strain along the a and b crystal axes. We analyzed the band-gap evolution as function of the deformation percentage, ranging from 1% to 8%. Results show that the system behaves as a direct band-gap semiconductor, with the valence band maximum and conduction band minimum located at the K point (1/3, 1/3, 0) of the Brillouin zone. This behavior is unchanged despite the strain application. The band gap underestimation, as computed within the standard DFT, was corrected by applying the G(0)W(0) approach. Trends in the band-gap behavior are the same within both approaches: for low deformation percentages, the band-gap grows linearly with a small slope, and at higher values, it grows very slow with a tendency to achieve saturation. Therefore, the band-gap is less sensitive to tensile strain for deformations near 8%. The origin of this band gap behavior is explained in terms of the projected density of states and charge densities, and it can be attributed to Coulomb interactions, and charge redistributions due to the applied tensile strain. To study the carrier mobility, we computed the electron and hole effective masses, finding high mobility for both carriers. Finally, the stability analysis of each strained system includes the calculation of phonon spectra, to assure the dynamical stability, the computation of elastic constants to evaluate the mechanical stability, and cohesive energies for exploring the thermodynamical stability. Results indicate that the boron phosphide monolayer is stable under the calculated tensile strains.
查看更多>>摘要：Melting behaviour of inorganic hydrated salts plays an important role in their application as phase change energy storage materials. Particularly, the phase transition temperature and latent heat are determining factors for their application in specific areas for building heating. Ionic salts (e.g. NaCl, KCl) have been proposed as additives to synthesize Glauber's salt with desired phase change properties. However, melting behaviour of the hydrated salts as well as the role of additives is poorly understood, which limits our ability to synthesize these salts with targeted properties. In the present study, classical molecular dynamics simulations were used to study the melting behaviour of pure Glauber's salt. System of NaCl center dot Na2SO4 center dot 10H(2)O was studied to gain insights into the atomistic mechanism of the ionic salt additives. It is observed that the transition of hydrated Glauber's salt into anhydrous Na2SO4 happens over a temperature range due to the stepwise dissociation of water molecules from the parent salt molecule. Addition of NaCl results in lowering the phase transition temperature, while increasing the latent heat of phase change at the same time. Simulation results showed that the hydrogen bonding capacity and ionic charge of the additive salts are the determining factors in altering the phase transition behaviour of hydrated salts. Simulation results showed an excellent agreement with the experimental data available in the literature.
Jia, TingPaudel, Hari P.Senor, David J.Duan, Yuhua...
5页
查看更多>>摘要：We performed first-principles calculations to study the H-3 diffusion in the zirconium hydrides with or without Sn impurity. Our results show that the formation of (ZrHx)-H-3 becomes preferable as the H-3 concentration increases. Based on the most stable configurations of (ZrHx)-H-3 (x = 0.5, 1.0, 1.5, 2.0), we studied the interstitial H-3 diffusion with or without Sn impurity. The results show that the interstitial H-3 diffusion becomes less probable in the hydrides with a higher H-3 concentration. When introducing a substitutional Sn impurity, the diffusion barriers increase. Therefore, the substitutional Sn in the diffusion pathway hampers the H-3 diffusion in Zr hydrides.
NSTL
Elsevier