Anisotropic Shock Response of 3,4-Dinitropyrazole Revealed by First-Principles Calculations.

DNP (3,4-dinitropyrazole) has attracted much interest due to its promising melting characteristics and high detonation performances, such as low melting point, high density, high detonation velocity, and low sensitivity. In this work, first-principles molecular dynamics (MD) simulations were performed to investigate the anisotropic shock response of DNP in conjunction with the multiscale shock technique (MSST). The initial decomposition mechanism was revealed through the evolution of the chemical reaction and product analysis. Independent gradients based on the Hirshfeld partition (IGMH) method showed that van der Waals forces mainly exist between the layered structures. Chemical reaction analyses revealed four major initial decomposition reactions for the DNP molecule. At different shock velocities, the molecules in $\left(\overline{1}01\right)$ were more inclined to undergo H dissociation reactions, whereas the molecules in $\left(\overline{1}0\overline{1}\right)$ were more inclined to undergo nitro-dissociation reactions. Product analysis showed that the faster the shock velocities, the earlier the DNP molecules completely disappeared. Furthermore, N₂ and CO₂ were mainly produced by the ring-opening reaction, and their numbers in $\left(\overline{1}01\right)$ were higher than in $\left(\overline{1}0\overline{1}\right)$, indicating that the ring-opening reaction was more easy to occur in $\left(\overline{1}01\right)$. The ring-opening reaction mainly occurred in $\left(\overline{1}01\right)$, suggesting that $\left(\overline{1}01\right)$ was more decomposable than $\left(\overline{1}0\overline{1}\right)$. The fitting results of the state equation showed that the theoretical detonation pressures for $\left(\overline{1}01\right)$ and $\left(\overline{1}0\overline{1}\right)$ are close to the experimental value. These results could help to increase the understanding of shock-induced anisotropy in energetic materials.