Abstract
The 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) is a newly energetic material with an excellent performance and low sensitivity and has attracted considerable attention. On the basis of the dispersion-corrected density functional theory (DFT-D), the high-pressure responses of vibrational properties, in conjunction with structural properties, are used to understand its intermolecular interactions and anisotropic properties under hydrostatic and uniaxial compressions. At ambient and pressure conditions, the DFT-D scheme could reasonably describe the structural parameters of LLM-105. The hydrogen bond network, resembling a parallelogram shape, links two adjacent molecules and contributes to the structure stability under hydrostatic compression. The anisotropy of LLM-105 is pronounced, especially for Raman spectra under uniaxial compression. Specifically, the red-shifts of modes are obtained for [100] and [010] compressions, which are caused by the pressure-induced enhance of the strength of the hydrogen bonds. Importantly, coupling modes and discontinuous Raman shifts are observed along [010] and [001] compressions, which are related to the intramolecular vibrational redistribution and possible structural transformations under uniaxial compressions. Overall, the detailed knowledge of the high-pressure responses of LLM-105 is established from the atomistic level. Uniaxial compression responses provide useful insights for realistic shock conditions.
Highlights
The density functional theory (DFT) calculations with DFT-D2 schemes significantly improved the description of the Molecules 2021, 26, 6831 crystal structure at ambient conditions
The calculated lattice parameters are in agreement with experimental values [5] and superior to previous first-principles calculations based on the force field [18] and parameterized CA-PZ and PW91 scheme [13], and close to the theoretical result by Zong et al [15]
The red-shifts of several vibrational modes are obtained under hydrostatic pressure due to the enhanced hydrogen bonds resulting from a reduced intermolecular distance
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Energetic materials (EMs), such as explosives, propellants, and pyrotechnics, are widely used for civilian and military purposes [1,2]. EMs can undergo multiple phase transitions during detonation, in which the molecules are modified and rearranged under high-temperature and high-pressure conditions. The evolutions of the pressure-dependent physical and chemical properties of EMs are important in the control of their sensitivity, performance, and safety [3,4]. 2,6-diamino-3,5-dinitropyrazine-1oxide (LLM-105), a new generation of high-energy and low-sensitivity EM, was synthesized by Lawrence Livermore Laboratories in the United States, and its foundational properties attracted attention
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