The response of high-energy-density materials to thermal or mechanical insults involves coupled thermal, mechanical, and chemical processes with disparate temporal and spatial scales that no single model can capture. Therefore, we developed a multiscale model for 1,3,5-trinitro-1,3,5triazinane, RDX, where a continuum description is informed by reactive and nonreactive molecular dynamics (MD) simulations to describe chemical reactions and thermal transport. Reactive MD simulations under homogeneous isothermal and adiabatic conditions are used to develop a reduced-order chemical kinetics model. Coarse graining is done using unsupervised learning via non-negative matrix factorization. Importantly, the components resulting from the analysis can be interpreted as reactants, intermediates, and products, which allows us to write kinetics equations for their evolution. The kinetics parameters are obtained from isothermal MD simulations over a wide temperature range, 1200−3000 K, and the heat evolved is calibrated from adiabatic simulations. We validate the continuum model against MD simulations by comparing the evolution of a cylindrical hotspot 10 nm in diameter. We find excellent agreement in the time evolution of the hotspot temperature fields both in cases where quenching is observed and at higher temperatures for which the hotspot transitions into a deflagration wave. The validated continuum model is then used to assess the criticality of hotspots involving scales beyond the reach of atomistic simulations that are relevant to detonation initiation.
Eco-friendly inorganic halide perovskite materials with numerous structural configurations and compositions are now in the leading place of researcher’s attention for outstanding photovoltaic and optoelectronic performance. In the present approach, density functional theory calculations have been performed to explore the structural, mechanical, electronic, and optical properties of perovskite-type CsGeCl3 under various hydrostatic pressures, up to 10 GPa. The result shows that the optical absorption and conductivity are directed toward the low-energy region (red shift) remarkably with increasing pressure. The analysis of mechanical properties certifies that CsGeCl3 has ductile entity and the ductile manner has increasing affinity with applied pressure. The decreasing affinity of the bandgap is also perceived with applied pressure, which notifies that the performance of the optoelectronic device can be tuned and developed under pressure.
All-inorganic cubic cesium germanium bromide (CsGeBr3) and cesium tin bromide (CsSnBr3) perovskites have attracted much attention because of their outstanding optoelectronic properties that lead to many modern technological applications. During their evolution process, it can be helpful to decipher the pressure dependence of structural, optical, electronic, and mechanical properties of CsXBr3 (X = Ge/Sn) based on ab initio simulations. The lattice parameter and unit cell volume have been decreased by applying pressure. This study reveals that the absorption peak of CsXBr3 (X = Ge/Sn) perovskites is radically changed toward the lower photon energy region with the applied pressure. In addition, the conductivity, reflectivity, and dielectric constant have an increasing tendency under pressure. The study of electronic properties suggested that CsXBr3 (X = Ge/Sn) perovskites have a direct energy bandgap. It is also found through the study of mechanical properties that CsXBr3 (X = Ge/Sn) perovskites are ductile under ambient conditions and their ductility has been significantly improved with pressure. The analysis of bulk modulus, shear modulus, and Young’s modulus reveals that hardness of CsXBr3 (X = Ge/Sn) perovskites has been enhanced under external pressure. These outcomes suggest that pressure has a significant effect on the physical properties of CsXBr3 (X = Ge/Sn) perovskites that might be promising for photonic applications.
Of late, inorganic perovskite material, especially the lead-free CsGeBr3, has gained considerable interest in the green photovoltaic industry due to its outstanding optoelectronic, thermal, and elastic properties. In this work, we systematically investigated the strain-driven optical, electronic, and mechanical properties of CsGeBr3 through the first-principles density functional theory. The unstrained planar CsGeBr3 compound demonstrates a direct bandgap of 0.92 eV at its R-point. However, by incorporating external biaxial tensile (compressive) strain the bandgap lowering (increasing) can be tuned to this perovskite. Moreover, due to the increase of tensile (compressive) strain, a red-shift (blue-shift) behavior of the absorption-coefficient and dielectric function is found in the photon energy spectrum. Strain-induced mechanical properties also reveal that CsGeBr3 perovskites are mechanically stable and highly ductile material and can be made suitable for photovoltaic applications. The strain-dependent optoelectronic and mechanical behaviors of CsGeBr3 explored here would be beneficial for its future applications in optoelectronics and photovoltaic cells design.
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