查看更多>>摘要：In this paper, atomistic simulations based on molecular dynamics (MD) are used to calculate the diffusion coefficients of xenon, uranium and oxygen in uranium dioxide containing different percentages of xenon atoms replaced by uranium from 2%Xe to 10%Xe at ten temperatures between 300 and 2500 K (covering three temperature regimes of athermal, intermediate and intrinsic). Since we did not take the irradiation conditions into account in the simulations, the calculated diffusion coefficients are "out-of-pile". Initially, the validity of the interatomic potential was performed by calculating the formation energies of interstitial, vacancy, Frankel and Schottky defects by using molecular statics (MS) simulations. Then, the migration energies of Xe/U/O based on considering various mechanisms were obtained by employing the Nudge Elastic Band (NEB) method. The results were generally in good agreement with those reported in the literature and the potential was validated. The simulations of UO2 containing different percentages of xenon (percentage of replacement of uranium atoms with xenon atoms) from 2 to 10 showed that with increasing the xenon percentage, the number of xenon clusters, cluster size, and radius of gyration considerably increases, and bubble nucleation was considerable in the case of 10%Xe. Then, by determining the slope of the mean square displacements, diffusion coefficients of xenon, uranium and oxygen were obtained. The results showed that they are both temperature-dependent and also dependent on the percentage of xenon (which was previously assumed to be independent of concentration). In the end, three temperature and xenon percentage dependent equations were proposed for the diffusion coefficients of xenon, uranium and oxygen. Finally, by applying a reduction factor (constant) to the diffusion coefficients, they were compared with experimental data available in the literature and significant satisfaction was obtained.
查看更多>>摘要：The shrinkage of sodium-poly(acrylate) PAA in divalent salt (strontium chloride (SrCl2) and barium chloride (BaCl2) solutions is investigated by atomistic molecular dynamics (MD) simulations to study the salt effect on PAA structure. The salt concentration (Cs) was varied in the range of 0 < Cs < 1 M for fully charged PAA. The PAA radius-of-gyration (Rg) decreases with Cs in the presence of both the divalent salts in qualitative agreement with experiments. The PAA chain stiffness calculated in persistence length (Lp) decreases over the entire range of Cs. At lower Cs, the PAA chains don't form aggregate, while at higher salt concentrations, PAA chains undergo self-association in both the divalent salts. The PAA-Water H-bonds decreases with Cs significantly in the presence of BaCl2 as compared to SrCl2. The PAA-Na+ radial distribution function (RDF) shows a decrease in its coordination number with Cs. The distribution of salt-ions around PAA shows that the Ba2+ condensation onto PAA is more significant than Sr2+ because of a greater coordination number for the former than the latter. Overall, the present study significantly advanced the molecular-level understanding of PAA microstructure in the dilute divalent metal salt solution.
Katoch, NehaKumar, JagdishKumar, AshokAhluwalia, P. K....
8页
查看更多>>摘要：Boron-based 2D monolayers have attracted tremendous interest due to their unique physical and chemical properties. In this paper, we report novel pentagonal monolayers, B2S and B2Se, which are predicted to be energetically, dynamically, and thermally stable based on density functional theory. At the HSE06 level of theory, they exhibit a moderate indirect bandgap of (e.g., 1.82 eV for Penta-B2S and 1.94 eV for Penta-B2Se). Strain-induced indirect-to-direct bandgap transition, high hole mobility (similar to 103 Cm2V- 1S- 1) and strong optical absorption (alpha similar to 105 Cm- 1) in the visible region are observed for these monolayers. Moreover, the electronic band structures and optical spectra are tunable by mechanical strains suggesting their visible light-harvesting capabilities for optoelectronic applications. In this way, the pentagonal family of 2D materials is now expanded to include boron-containing photocatalytic materials for water splitting applications.
查看更多>>摘要：The electronic structure and thermoelectric properties of bulk to monolayer BiSbS3 are studied by density functional theory and semi-classical Boltzmann transport equation. Meanwhile, it is clear that bulk and mono-layer BiSbS3 are semiconductors with indirect band gaps by using the TB-mBJ scheme, respectively. Further, it can be known that the phonon spectrum of thin film BiSbS3 has no negative frequency, and it can be inferred further that thin film BiSbS3 is stable. Monolayer BiSbS3 studied in this paper has extremely low lattice thermal conductivity at room temperature, which is lower than that of single quintuple layer Bi2Te3, bulk Sb2Te3, single-QL Bi2Se3 and Bi2Te3S at room temperature. The maximum figure of merit of p-type monolayer BiSbS(3)is obtained at a temperature of 1100 K and carrier concentration of 1 x 10(20) cm(-3). The optimal figure of merit, which is procured from n-type monolayer BiSbS3 within the range of carrier concentration interval considered in this paper, is obtained at 1500 K and 5 x 1019 cm(-3).
查看更多>>摘要：We present mechanoChemML, a machine learning software library for computational materials physics. mechanoChemML is designed to function as an interface between platforms that are widely used for machine learning on one hand, and others for solution of partial differential equations-based models of physics. Of special interest here, and the focus of mechanoChemML, are applications to computational materials physics. These typically feature the coupled solution of material transport, reaction, phase transformation, mechanics, heat transport and electrochemistry. Central to the organization of mechanoChemML are machine learning workflows that arise in the context of data-driven computational materials physics. The mechanoChemML code structure is described, the machine learning workflows are laid out and their application to the solution of several problems in materials physics is outlined.
查看更多>>摘要：In this study, the mechanical properties of a graphene/aluminum (Gr/Al) composite under uniaxial tension and compression were investigated using molecular dynamics (MD) simulations. Six different simulation models were used to investigate whether the addition of graphene significantly improved the stiffness and strength of Gr/Al composites. Moreover, the results show that the existence of a graphene layer can effectively prevent the propagation of dislocations at the interface, thus improving the mechanical properties of the composites. The deformation mechanism of the composites was studied by comparing the effects of the deformation behavior, compressive stress, and dislocation. The dislocation movement of the Al matrix during compression was further investigated. It was determined that stair-rod and Hirth dislocations occurred in the Al matrix, and the graphene layers exhibited bulging and kink deformation. Furthermore, the mean curvature and Gaussian curvature of the compressed graphene surface were measured, and the deformation characteristics of graphene in the composites were considered using the geometric method. We applied a new method to calculate the surface curvature and mechanical material deformation.
查看更多>>摘要：We present a Monte Carlo (MC) approach to solve the phonon Boltzmann transport equation (BTE) in which the anisotropic phonon dispersion relations over the full Brillouin zone (BZ) are used. In this approach, the discretization of the BZ used to compute the phonon relaxation time places constraints on the direction of scattered phonons in the real-space simulation domain. The phonon dispersion and phonon relaxation times are calculated using the density functional theory (DFT) approach. The modified MC approach is validated by a close examination of its ability to simulate phonon transport in both the ballistic and diffusive regimes for multiple materials including GaAs, InAs, ThO2, and alpha-U. In doing so, the phonon thermal conductivities from 100 K to 1000 K are calculated and compared with traditional non-transport solution of the phonon BTE. It is found that the phonon thermal conductivities of alpha-U and ThO2 obtained from MC simulations using isotropic dispersion are larger than the values obtained using anisotropic phonon dispersion relations over the full BZ. The effect of phonon-defect scattering on the thermal conductivity of ThO2 is also studied as an application of the current MC approach and found to agree with previously computed values in the literature. The MC solver developed here has been parallelized as a step to demonstrate its potential to solving computationally intensive phonon thermal transport problems at the mesoscale.
Reis, Marie Landeiro DosGiret, YvelinCarrez, PhilippeCordier, Patrick...
10页
查看更多>>摘要：This study focuses on the mechanisms of pipe diffusion and the kinetic of point defect diffusion along dislocation line in MgO. We developed a numerical approach, based on atomic scale calculations and the use of the elasticity theory, to determine the migration energies of point defects. The kinetic of diffusion along the dislocation is then evaluated according to a on-lattice atomistic kinetic Monte Carlo algorithm informed by atomistic simulations. We show that edge dislocation in MgO behaves as a strong sink for vacancies which, combined with a lower migration energy at dislocation core region, strongly enhances the diffusion of point defect in the vicinity of the dislocation with respect to the bulk material. At low and intermediate temperatures, pipe diffusion results in an increase of the diffusivity of several order of magnitude. Accounting more precisely for the effect of pipe diffusion may therefore be a key to reconcile the experimentally measured scattering of diffusivity in MgO.
查看更多>>摘要：Molecular dynamics simulations of graphene (G) or graphene oxide (GO) plates with epoxy, PDMS, or ABS were separately performed to investigate plate/polymer interactions. The interactions were qualitatively assessed in larger models by visual observation of a G or GO plate's orientation with respect to polymer surfaces. They were also quantitatively evaluated in smaller models for changes in potential and non-bonding energy during mixing. The quantitative simulations allowed for the determination of energies of interaction that could not be detected in the larger qualitative studies, including aspects of plate alignment with respect to the polymer at the initiation of interactions. Both the qualitative and quantitative simulations independently demonstrated polymer matrix plate composites (PMPCs) doped with GO resulted in greater stabilizing interactions than those doped with G. In epoxy and ABS, GO showed 40-50% stronger interactions than G, while in PDMS, G had a strong de-stabilizing effect.
Ghumman, Umar Farooqvan Beek, AntonMunshi, JoydeepChien, TeYu...
11页
查看更多>>摘要：Molecular dynamics simulations have shown substantial promise in the design of organic photovoltaic cells (OPVC). Despite their potential, the utility of molecular dynamics simulations when designing an OPVC is often limited due to their considerable computational cost and their limited prediction accuracy. To address these challenges, we introduce a three-step multi-fidelity design framework that enables a designer to efficiently explore the space of admissible processing conditions, using coarse-grained molecular dynamics (CGMD) sim-ulations, to identify the optimal OPVC design. Using a novel spectral density based approach to reconstruct microstructures of variable size, the framework is able to sequentially search for the globally optimal micro-structure using a low-fidelity CGMD simulation with a smaller window size, followed by the optimization of the processing conditions using the high-fidelity simulation. The division in two steps and two fidelities enables the optimization of CGMD simulations at previously intractable lengths and timescales. We validate our results by demonstrating that the CGMD model predictions are consistent with physical experiments reported in the literature and corroborate that the computational complexity is reduced by one order of magnitude.
NSTL
Elsevier