Modeling Thermal Decomposition Mechanisms in Gaseous and Crystalline Molecular Materials: Application to β-HMX

Abstract

Exploration of initiation of chemistry in materials is especially challenging when several coexisting chemical mechanisms are possible and many reactions' products are produced. It is even more difficult for complex materials, such as molecular, supramolecular, and hierarchical materials and systems. A strategy to draw a complete picture of the earliest stages of rapid decomposition reactions in molecular materials is presented in this study. The strategy is based on theoretical and computational modeling of chemical decomposition reactions in the gaseous and crystalline molecular material that has been performed by means of combined density functional theory and transition state theory. This study reveals how a crystalline field affects materials chemical degradation. We also demonstrate how incomplete results, which are often used due to difficulties in obtaining comprehensive data, can lead to erroneous conclusions and predictions. We discuss our approach in the context of the obtained reaction energies, activation barriers, structures of transition states, and reaction rates with the example of a representative molecular material, β-HMX, which tends to decompose violently with large energy release upon an external perturbation. The performed analysis helps to provide a consistent interpretation of available experimental data. The article illustrates that the complete picture of decomposition reactions of complex molecular materials, while theoretically challenging and computationally demanding, is possible and even practical at this point in time.

Comparative analysis of decomposition reactions in gaseous and crystalline -HMX

“…Details of all possible decomposition mechanisms in gas-phase and solid-phase ideal HMX are discussed elsewhere [7,8].…”

Dynamic Responses and Initial Decomposition under Shock Loading: A DFTB Calculation Combined with MSST Method for β-HMX with Molecular Vacancy

“…Many experimental and theoretical studies suggested that the N−NO 2 bond fission had the lowest energy barriers. 10,22 However, the N−N bond was significantly compressed at high pressure. 13,16 It was still contradicted which one was the dominant pathway among these reaction models.…”

Searching for new energetic materials: Computational design of novel nitro-substituted heterocyclic explosives

“…Minimal energy paths were investigated by conducting intrinsic reaction coordinate computations using the Hessian-based Predictor-Corrector integrator algorithm 22 for each transition state. Reaction rates were calculated by applying transition state theory (TST) 23 for reactions with well-defined transition states and variational TST 24 for reactions with no barriers as detailed elsewhere 11,12,13 .…”

“…a clear understanding of the relationships between thermal stability of materials, their molecular and crystalline structures, and chemical properties remain unachieved 8 . With tremendous progress in the development of computer hardware and computational algorithms, theoretical modeling has become a powerful tool for exploration of physicochemical properties of explosive materials including the geometry and electronic structure, 9,10 thermal stability, 11,12,13 and the materials' response to mechanical impact 14,15,16 . A close collaboration between synthetic chemists, researchers who perform advanced characterization tests of materials, and those who analyze materials with theoretical and computational quantum-chemical methods prove to be particularly effective1 ,17 .…”