Periodic density functional theory with dispersion correction (DFT-D) was used to study the structural, electronic, and absorption properties of crystalline 5-nitramino-3, 4-dinitropyrazole (NADNP) under hydrostatic compression of 0-140 GPa. The results indicate that the PBE-G06 is the best functional for studying NADNP. As the pressure increases, the lattice of parameters, band gap, density of states and absorption spectra change regularly except for 126 GPa, where NADNP begins to decompose and form a new bond. An analysis of the band gap and density of states indicates that NADNP becomes more and more sensitive under compression. The absorption spectra show that NADNP has relatively high optical activity with increasing pressure.

Ab initio molecular dynamics simulations were performed to study the initiation of decompositionand formation of first products of two molecular crystals pentaerythritol tetranitrate (PETN) and 5-nitro-2,4-dihydro-1,2,4-triazole-3-one (NTO) under thermal decomposition temperature (475 K for PETN and 531 Kfor NTO) coupled with different pressures (1-5 GPa). The pressure effects on the initial decomposition stepsand initially generated products on PETN and NTO were very different. PETN was triggered by C-H... O intermolecular hydrogen transfer. The initial decomposition mechanism was independent of the pressure. ForNTO, two different initial decomposition mechanisms were found. At 1, 2, and 3 GPa, it was triggered by NH....O intermolecular hydrogen transfer, while at 4 and 5 GPa, it was triggered by N-H.....N intermolecularhydrogen transfer. This indicates that the initial decomposition mechanism was dependent on the pressure.Our study may provide new insights into initial mechanisms and decomposition reactions of molecular crystalexplosives under thermal decomposition temperature coupled with different pressures with details at atomiclevel.