Review of the molecular and crystal correlations on sensitivities of energetic materials.

2,6-Diamino-3,5-dinitropyrazine-1-oxide (LLM-105) was first synthesized about 20 years ago and is regarded as a representative of the new generation of low-sensitivity energetic materials (EMs). Nevertheless, its thermal decay detail still remains lacking; in particular, the atomistic details of the decomposition of its condensed phase are absent. Thus, this work presents a quantum chemistry based study to reveal the details. Four pathways are found to initiate the primary molecular fission, including the intramolecular H transfer from a NH2 group to its neighboring acyl O atom, the NO2 partition, the acyl O partition, and the O partition from a NO2 group. The dominance of these pathways is strongly temperature-dependent, i.e., the intramolecular H transfer and the NO2 partition govern the initial steps at relatively low and high temperatures, respectively, and both the O partitions each occur once only at high temperature. Furthermore, we find that the intramolecular H transfer takes place always with a ...

Reversible Hydrogen Transfer as New Sensitivity Mechanism for Energetic Materials against External Stimuli: A Case of the Insensitive 2,6-Diamino-3,5-dinitropyrazine-1-oxide

We report dispersion-corrected density functional theoretical calculations of the unreacted equation of state (EOS) of crystal 2,6-diamino-3, 5-dinitropyrazine-1-oxide (LLM-105) under hydrostatic compression of up to 45 GPa. Convergence tests for k-points sampling in the Brillouin zone show that a 3 × 1 × 2 mesh is required to reproduce the X-ray crystal structure at ambient conditions, and we confirm our finding with a separate supercell calculation. Our high-pressure EOS yields a bulk modulus of 19.2 GPa, and indicates a tendency towards anisotropic compression along the b lattice vector due to molecular orientations within the lattice. We find that the electronic energy band gap decreases from a semiconductor type of 1.3 eV at 0 GPa to quasi-metallic type of 0.6 eV at 45 GPa. The extensive intermolecular hydrogen bonds involving the oxide (–NO) and dioxide (–NO2) interactions with the amine (–NH2) group showed enhanced interactions with increasing pressure that should be discernible in the mid IR spectral region. We do not find evidence for structural phase transitions or chemically induced transformations within the pressure range of our study. The gas phase heat of formation is calculated at the G4 level of theory to be 22.48 kcal/mol, while we obtain 25.92 kcal/mol using the ccCA-PS3 method. Density functional theory calculations of the crystal and the gas phases provided an estimate for the heat of sublimation of 32.4 kcal/mol. We thus determine the room-temperature solid heat of formation of LLM-105 to be −9.9 or −6.5 kcal/mol based on the G4 or ccCA-PS3 methods, respectively.

First-principles high-pressure unreacted equation of state and heat of formation of crystal 2,6-diamino-3, 5-dinitropyrazine-1-oxide (LLM-105)

Recent theoretical studies of 2,6-diamino-3,5-dinitropyrazine-1-oxide (C4H4N6O5 Lawrence Livermore Molecule No. 105, LLM-105) report unreacted high pressure equations of state that include several structural phase transitions, between 8 and 50 GPa, while one published experimental study reports equation of state (EOS) data up to a pressure of 6 GPa with no observed transition. Here we report the results of a synchrotron-based X-ray diffraction study and also ambient temperature isobaric-isothermal atomistic molecular dynamics simulations of LLM-105 up to 20 GPa. We find that the ambient pressure phase remains stable up to 20 GPa; there is no indication of a pressure induced phase transition. We do find a prominent decrease in b-axis compressibility starting at approximately 13 GPa and attribute the stiffening to a critical length where inter-sheet distance becomes similar to the intermolecular distance within individual sheets. The ambient temperature isothermal equation of state was determined through refinements of measured X-ray diffraction patterns. The pressure-volume data were fit using various EOS models to yield bulk moduli with corresponding pressure derivatives. We find very good agreement between the experimental and theoretically derived EOS.

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The high pressure structure and equation of state of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) up to 20 GPa: X-ray diffraction measurements and first principles molecular dynamics simulations

The new energetic material 2,6-diamino-3,5-dinitropyrazine-1-oxide (C4H4N6O5, LLM-105) maintains its structural stability under high pressure below 30 GPa at room temperature or in the temperature ...

Pressure- and Temperature-Dependent Structural Stability of LLM-105 Crystal

Periodic first-principles calculations have been performed to study the effect of high pressure on the geometric, electronic, and absorption properties of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) under hydrostatic pressures of 0–50 GPa. Obvious irregular changes in lattice constants, unit-cell angles, bond lengths, bond angles, and band gaps showed that crystalline LLM-105 undergoes four structural transformations at 8, 17, 25, and 42 GPa, respectively. The intramolecular H-bonds were strong at pressures of 0–41 GPa but weakened in the range 42–50 GPa. The lengths of the intermolecular H-bonds (<1.47 A) indicated that these H-bonds have covalent character and tend to induce the formation of a new twelve-membered ring. Analysis of the DOS showed that the interactions between electrons, especially the valence electrons, strengthen under the influence of pressure. The p states play a very important role in chemical reactions of LLM-105. The absorption spectrum of LLM-105 displayed more bands—as well as stronger bands—in the fundamental absorption region when the pressure was high rather than low. A new absorption peak due to O–H stretching appeared at 18.3 eV above 40 GPa, indicating that covalent O–H bonds and a new twelve-membered ring are present in LLM-105.

First-principles study of the structural transformation, electronic structure, and optical properties of crystalline 2,6-diamino-3,5-dinitropyrazine-1-oxide under high pressure

Density functional theory and volume-based thermodynamics calculations have been performed to study the crystal densities, heats of formation (HOFs), energetic properties, thermodynamics of formation, and impact sensitivity for the salts composed of heterocycle-functionalized nitraminofurazanate-based anions and triaminoguanidinium cation. The results show that the triaminoguanidinium nitraminofurazanate-based salts have high densities and positive HOFs. The substitution of the oxygen-containing substituent (−NO2 or −C(NO2)3) is helpful for enhancing the densities and detonation properties of the nitraminofurazanate-based salts, and the substitution of −C(NO2)3 exhibits the best performance. Incorporating the conjugated bridge −N═N– or −N═N–N═N– into the heterocycle-functionalized nitraminofurazanate-based salts is favorable for improving the density and detonation properties of its salt. The tetrazole-functionalized salts exhibit the best detonation properties among the three salt series. The calculated ...

Comparative Theoretical Studies on Energetic Ionic Salts Composed of Heterocycle-Functionalized Nitraminofurazanate-Based Anions and Triaminoguanidinium Cation

We have performed density functional theory and volume-based thermodynamics calculations to study the effects of different combinations of energetic anions and cations on the crystal densities, heats of formation, energetic properties, and thermodynamics of formation for a series of 5-nitroiminotetrazolate-based ionic salts. The results show that the substitution of the -NO2, -NF2, -N3, or -C(NO2)3 group is helpful for increasing the densities of the salts. Incorporating every substituent (-NH2, -NO2, -NF2, -N3, or -C(NO2)3) into the salt is favorable for improving its HOF and detonation performance. Incorporating the cation B1, B2, B10, or B11 into the salts is helpful for improving its detonation properties. Increasing negative charge for the 5-nitroiminotetrazolate-based salts is unfavorable for enhancing the density and detonation performance, but is helpful for increasing the HOFs. Many salts present comparable detonation performance with commonly used explosives RDX or HMX. Among them, 21 salts have near or better properties than HMX. The thermodynamics of formation of the salts show that the majority of the 5-nitroiminotetrazolate salts with the cation B1, B3, B9, B10, B12 could be synthesized by the proposed reactions.

Theoretical studies of energetic nitrogen-rich ionic salts composed of substituted 5-nitroiminotetrazolate anions and various cations

The structural, electronic, and absorption properties of crystalline β-FOX-7 were studied by density functional theory–generalized gradient approximation (GGA) and local density approximation (LDA) calculations. The results indicate that there are irregular changes occurred at 9, 17, 32, and 37 GPa for the GGA results and at 2, 7, 22, and 32 GPa for the LDA ones, in agreement with previous reports that the LDA generally underestimated, while the GGA overestimated the structure and properties of the crystals. The compression ratios of the lattice constants suggest that the structure of β-FOX-7 is much stiffer in a- and c-directions than in b-direction. The total decrease ratio of C–NO2 band lengths is larger than that of other bond lengths, indicating that the C–NO2 bond cleavage may trigger the initiation decomposition of β-FOX-7. An analysis of density of states suggests that the interactions between electrons are strengthened under the influence of pressure. The absorption spectra indicate that the bands in the fundamental absorption region have relatively high optical activity at high pressure.

Pressure-induced structure and properties of crystalline β-FOX-7 by LDA and GGA calculations

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Papers

First-principles study of the structural transformation, electronic structure, and optical properties of crystalline 2,6-diamino-3,5-dinitropyrazine-1-oxide under high pressure

Comparative Theoretical Studies on Energetic Ionic Salts Composed of Heterocycle-Functionalized Nitraminofurazanate-Based Anions and Triaminoguanidinium Cation

Theoretical studies of energetic nitrogen-rich ionic salts composed of substituted 5-nitroiminotetrazolate anions and various cations

Pressure-induced structure and properties of crystalline β-FOX-7 by LDA and GGA calculations