Temperature-dependent Raman spectroscopy and thermodynamic behaviors of energetic NTO crystal

The vibrational and thermodynamic properties of energetic materials (EMs) are critical to understand their structure responses at finite temperature. In this work, the zero-point energy and temperature effects are incorporated into dispersion-corrected density functional theory to improve the calculated accuracy for vibrational responses and thermodynamic behaviors of 3-nitro-1,2,4-triazole-5-one (NTO). Based on temperature-dependent Raman spectroscopy, the emergence and disappearance of new peaks as well as discontinuous Raman shifts indicate the distinct changes of molecular configuration and intermolecular interactions within the temperature of 250-350 K. From Hirshfeld surface and structure analysis, the subtle changes of intermolecular hydrogen bonds (HBs) related with the shrinkage of thermal expansion coefficient, are treated as an essential step of a potential structural transformation of NTO. Moreover, the calculated heat capacity, entropy and bulk moduli could reflect the softening behavior of NTO and further enrich the thermodynamic data set of EMs. These results demonstrate the evolution of NTO molecules controlled by non-covalent interactions and provide vital insights into the thermodynamic behaviors at finite temperature.

Reactive molecular dynamics simulations on the decomposition process of 1,3,5-trinitro-1,3,5-triazine crystal under high temperatures and pressure

CONTEXT

Reactive molecular dynamics simulations were performed to study the decomposition processes of 1,3,5-trinitro-1,3,5-triazine (RDX) crystal under high temperatures (2100, 2400, 2700, and 3000 K) and detonation pressure (34.5 GPa) and 0 GPa. It is found that the initial decomposition paths of RDX under different temperatures coupled with detonation pressure are similar, which is due to the N-NO2 bond breakage to release NO2. The formation rates of N2 and H2O are significantly affected by temperature, while those of CO2 are less influenced. The C atoms finally formed C clusters. As the temperature rises, the decomposition speeds up, indicating that the high temperature accelerates the decomposition. Applying pressure can reduce the reaction energy barrier and accelerate the decomposition.

METHODS

The RDX model was constructed using the Materials Studio 7.0 package. All MD simulations were performed based on the ReaxFF force field in the LAMMPS software package, and the crystals were visualized using the OVITO software package. The time step was 0.1 fs, and the total MD simulation time was 200 ps. DFT calculations were carried out at the B3LYP/6-311G(d,p) level using the Gaussian 09 package.

Pressure-dependent structure and electronic properties of energetic NTO crystals dominated by hydrogen-bonding interactions

3-Nitro-1,2,4-trihydroxy-5-one (NTO), a highly potential high-performance explosive with good thermal stability and low sensitivity, has attracted much attention for its physicochemical properties in recent years. In this work, the pressure effect of the vibrational and electronic properties is investigated to understand the intermolecular interaction of NTO under hydrostatic compression. From the pressure-dependent Raman and infrared spectra, we found that the red-shifts of high-wavenumber N-H stretching modes and the discontinuous shifts of all Raman modes occur at 3 and 6 GPa, indicating an evident change of molecular configuration and intermolecular interaction upon compression. Based on structural analysis, the changes of intra- and intermolecular hydrogen bonds (HBs) are closely relevant to the anomalous rotation of the nitro group and the lengthening of N-H bonds, which can be treated as an important step of a potential structural transformation of NTO. Moreover, intermolecular hydrogen-bonding interaction leads to the shrinkage of the band gap at 6 GPa, caused by the fast charge transfer of 0.07 e from the nitrogen heterocycle to the nitro group. These results manifest a non-covalent interaction mechanism for modulating the molecular configuration of EMs under pressure loading and provide vital insights into understanding the pressure effects for energetic molecular crystals.

Thermal decomposition mechanisms of energetic CL-20-based co-crystals: quantum molecular dynamics simulations

The decomposition mechanisms of energetic CL-20:2,4-dinitro-2,4-diazapentane (DNP) and CL-20:2,4-dinitro-2,4-diazaheptane (DNG) co-crystals at high temperatures (1000, 2000, and 3000 K) were studied by density functional tight-binding molecular dynamics (DFTB-MD) simulations. At different temperatures, their decomposition mechanisms are very different. At 1000 K, conformational changes are observed only for the CL-20:DNG co-crystal, in which the CL-20 changes from β-CL-20 to γ-CL-20. When the temperature is increased to 2000 K, CL-20, DNP, and DNG begin to decompose, and there are five paths for the main initial mechanisms. Further increasing the temperature to 3000 K promotes a more complete decomposition. The initial reactions of CL-20 in the two co-crystals have two channels. There are two initial decomposition channels in the DNP molecule and only one channel in the DNG molecule. As the temperature increases, the decomposition products of the two co-crystals are different. Our work may provide the in-depth understanding of the decomposition mechanisms of high-energy CL-20-based co-crystals at high temperatures.

Structural stability and initial decomposition mechanisms of BTF crystal induced by vacancy defects: a computational study

Density functional tight binding (DFTB) and DFTB-based molecular dynamics (DFTB-MD) were used to study the effects of vacancy defects on the structure, stability, and initial decomposition mechanisms of condensed phase...

Recent advances in studying the nonnegligible role of noncovalent interactions in various types of energetic molecular crystals

This highlight summarizes the research progress on the considerable effects of noncovalent interactions on diverse types of energetic materials and enlighten us to explore new factors that affect the key performance of explosives.

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

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.