Temperature and pressure effects on the decomposition mechanisms of 2,6-diamino-3,5-dinitropyrazine-1-oxide crystal: ab initio molecular dynamics study

Context

The decomposition process of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) crystal at high temperatures (2500 and 3390 K) and detonation pressure of 33.4 GPa coupled with temperatures were studied by ab initio molecular dynamics simulations. The results show that the initial decomposition mechanism of LLM-105 is the same under different conditions. The product analysis indicates that high temperature is conducive to the formation of N₂ and CO₂, but inhibited the formation of H₂O. It is found that the formation mechanism of H₂O is the same under different conditions, which involves the reaction between OH radical and H radical. Although the detailed processes of the formation of N₂ are different, they all involve the reaction between nitrogen-containing fragments, and its core is the formation of intermediates with R₁-NN-R₂ structure. The core of the formation of CO₂ under different conditions is to form the intermediate R₁-CO-R₂ with carbonyl structure, and then generate the fragment with -OCO- structure, and finally generate CO₂. This research may provide new insights into the initiation and subsequent decomposition mechanisms of energetic materials under extreme conditions.

Methods

The LLM-105 supercell was constructed using the Materials Studio 7.0 package. AIMD simulations were performed in the CASTEP package. AIMD simulations adopted NVT and NPT ensemble, and the temperature was controlled by Nosé thermostat, while the pressure was controlled by Andersen barostat. Besides, DFT calculations were carried out at the B3LYP/6–311 + G(d,p) level using the Gaussian 09 package.