Review of the Current Synthesis and Properties of Energetic Pentazolate and Derivatives Thereof

The inherent contradiction between the energy density and safety of energetic materials (EMs) is very challenging. To solve this problem, cocrystallization technology has been usually used in the f...

Nitramine-Based Energetic Cocrystals with Improved Stability and Controlled Reactivity

We have performed quantum-based multiscale simulations to study the initial chemical processes of condensed-phase octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) under shock wave loading. A self-consistent charge density-functional tight-binding (SCC-DFTB) method was employed. The results show that the initial decomposition of shocked HMX is triggered by the N–NO₂ bond breaking under the low velocity impact (8 km/s). As the shock velocity increases (11 km/s), the homolytic cleavage of the N–NO₂ bond is suppressed under high pressure, the C–H bond dissociation becomes the primary pathway for HMX decomposition in its early stages. It is accompanied by a five-membered ring formation and hydrogen transfer from the CH₂ group to the −NO₂ group. Our simulations suggest that the initial chemical processes of shocked HMX are dependent on the impact velocity, which gain new insights into the initial decomposition mechanism of HMX upon shock loading at the atomistic level, and have important implications for understanding and development of energetic materials.

Initial Decomposition of the Condensed-Phase β-HMX under Shock Waves: Molecular Dynamics Simulations B

Abstract Cocrystallization is an important method to obtain high-energy and low-sensitivity explosives. Therefore, the synthesis, structures, and properties of cocrystal energetic materials have become a highly active research topic. Studying the physical and chemical properties of cocrystal energetic materials by molecular dynamics is of great significance for the in-depth understanding and design/synthesis of new cocrystal energetic materials. This review introduces the method of molecular dynamics, the cocrystal energetic materials synthesized successfully to date, and the application of molecular dynamics to cocrystal energetic materials. The existing problems and future development directions are discussed. We hope that this review will encourage researchers interested in the field to design and synthesize high-energy and low-sensitive energetic materials with practical application value.

https://www.degruyter.com/document/doi/10.1515/ntrev-2022-0124/pdf

Molecular dynamics application of cocrystal energetic materials: A review

A neural network potential (NNP) is developed to investigate the complex reaction dynamics of 1,3,5-trinitro-1,3,5-triazine (RDX) thermal decomposition. Our NNP model is proven to possess good computational efficiency and retain the ab initio accuracy, which allows the investigation of the entire decomposition process of bulk RDX crystals from an atomic perspective. A series of molecular dynamics (MD) simulations are performed on the NNP to calculate the physical and chemical properties of the RDX crystal. The results show that the NNP can accurately describe the physical properties of RDX crystals, such as the cell parameters and the equation of state. The simulations of RDX thermal decomposition reveal that the NNP could capture the evolution of species at ab initio accuracy. The complex reaction network was established, and a reaction mechanism of RDX decomposition was provided. The N-N homolysis is the dominant channel, which cannot be observed in previous DFT studies of isolated RDX molecule. In addition, the H abstraction reaction by NO2 is found to be the critical pathway for NO and H2O formation, while the HONO elimination is relatively weak. The NNP gives an atomic insight into the complex reaction dynamics of RDX and can be extended to investigate the reaction mechanism of novel energetic materials.

Revealing the thermal decomposition mechanism of RDX crystals by a neural network potential.

The cocrystallization effect plays a prominent role in improving the performance of energetic materials. A combinational strategy based on density functional tight-binding molecular dynamics (DFTB-...

Conformational Changes and Decomposition Mechanisms of HMX-Based Cocrystal Explosives at High Temperatures

As a significant stimulus, the external electric field (EEF) plays a vital role in affecting the behaviors of energetic materials (EMs). We investigated the effects of the EEF on CL-20/HMX cocrystal and its pure components by molecular dynamics simulations. The COMPASS force field, atom-based summation method for van der Waals interactions, and Ewald summation method for electrostatic forces were applied. The results show that there exists sudden conformational changes at the EEF intensity of 0.3 and 0.9 V/A for β-HMX and e-CL-20, respectively, while the EEF-induced conformational change in CL-20/HMX is a gradual process. The analysis of the N-NO2 bond length distributions, radial distribution functions (RDFs) of the intermolecular O⋯H atom pair, and cohesive energy density (CED) reveals that the EEF can remarkably decrease the N-NO2 bond length and enhance hydrogen bonding interactions in the systems. A comprehensive analysis of the structural stability based on the maximum bond length of the trigger bond (Lmax), the interaction energy between two N atoms of the N N trigger bond (EN-N), and mechanical properties indicates that EEF can effectively improve the stability of the systems. These findings provide basic insights into the comprehensive understanding of the effects of the EEF on the EMs.

External electric field induced conformational changes as a buffer to increase the stability of CL-20/HMX cocrystal and its pure components

Molecular design of all nitrogen pentazole‐based high energy density compounds with oxygen balance equal to zero

Nanoparticles (NPs) possess the unique physical and chemical properties compared with gas-phase molecule and bulk crystal. Hence, the energetics, electronic structure, and vibrational properties of CL-20 and NTO NPs were investigated by the combinational strategy based on density-functional tight-binding (DFTB) and density-functional theory (DFT) methods. The results show that NPs possess quite different features from the isolated state molecule and the bulk crystal. The excess energies, surface energies, and enthalpy of sublimation for the NPs are predicted. The surface-induced surface states of the CL-20 and NTO NPs result in the significant decrease on the energy gaps and the formation of active sites on the surfaces. The vibrational properties related to the decomposition pathways for both CL-20 and NTO NPs, gas molecules, and bulk crystals are discussed and compared with previous theoretical and experimental values. Our results are expected to provide basic insights into the understandings of the surface effect of nano-sized energetic materials.

Theoretical studies of size effects on surfacial properties for CL-20 and NTO nanoparticles

The cocrystallization effect plays a prominent role in improving the performance of energetic materials. A combinational strategy based on density functional tight-binding molecular dynamics (DFTB-MD) simulations and density functional theory (DFT) was used to elucidate the decomposition mechanisms and reaction kinetics of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)-based cocrystal explosives [HMX/N,N-dimethylformamide (DMF) and HMX/bis(2,4-dinitro-2,4-diazapentane) (DNDAP)] at high temperatures. The decomposition and reaction mechanisms of the two cocrystals showed great dependence on the temperature. In the HMX/DMF cocrystal, a conformational change of HMX at 2000 K and subsequent initial decomposition of HMX at 2500 K is involved. At 3000 K, the global decomposition and interaction of the HMX and cocrystal molecules occurred. There are two dominant competing reaction channels in the two cocrystals. The comparative results reveal that the HMX molecules have a larger reactivity with DNDAP at low temperatures but with DMF at high temperatures. The decomposition pathways of the HMX molecules based on DFT calculations were studied as a useful addition to the MD results. These findings provide a basic understanding of the thermal decomposition mechanisms and reaction kinetics of HMX-based cocrystal energetic materials at high temperatures.

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Conformational Changes and Decomposition Mechanisms of HMX-Based Cocrystal Explosives at High Temperatures

External electric field induced conformational changes as a buffer to increase the stability of CL-20/HMX cocrystal and its pure components

Molecular design of all nitrogen pentazole‐based high energy density compounds with oxygen balance equal to zero

Theoretical studies of size effects on surfacial properties for CL-20 and NTO nanoparticles

Conformational Changes and Decomposition Mechanisms of HMX-Based Cocrystal Explosives at High Temperatures