Chen Jun, Xu Jiani, Xiao Tingting, Ma Peng, Ma Congming
College of Safety Science and Engineering, Nanjing Tech University, Nanjing, 211816, China.
J Mol Model. 2024 Nov 7;30(12):395. doi: 10.1007/s00894-024-06197-4.
Based on the density functional theory (DFT), we analyzed the changes of the FOX-7 molecule under external electric field (EEF) from multiple perspectives, including molecular structure, electronic structure, decomposition mechanism, frontier molecular orbitals (FMOs), and density of states (DOS). The results revealed that as the intensity of the positive EEF increased, the detonation performance of the FOX-7 molecule was significantly enhanced, while its thermal stability was also improved. This discovery challenges the traditional concept that explosives are inherently dangerous under external electric fields and provides new insights for research in related fields. To further explore the impact of EEF on the thermal stability of FOX-7, we conducted a thorough analysis of the mechanism by which EEF affects the decomposition process. Our findings indicate that applying a positive EEF significantly increases the energy required to overcome intramolecular hydrogen transfer and C-NO bond rupture, while having a relatively minor effect on the nitro isomerization process. This observation further demonstrates that the appropriate application of a positive EEF can enhance the detonation performance of FOX-7 without compromising its thermal stability. Further research revealed that as the intensity of the positive EEF increased, the electronegativity of the nitro group gradually enhanced, leading to an increase in the electronegativity of the oxygen atoms within it. This made the oxygen atoms more prone to participating in chemical reactions. This phenomenon also explains why the energy barrier required for nitro isomerization in FOX-7 gradually decreases as the intensity of the positive EEF increases.
Based on the density functional theory (DFT), the structural optimizations were performed both under applied EEF and without EEF at the B3LYP/6-311G (d, p) level. All optimized results were converged and exhibited no imaginary frequencies. Based on the optimized structures, single-point energy calculations were further conducted at the B3LYP/def2-TZVPP level. Subsequently, analyses of molecular structure, electronic structure, decomposition mechanism, frontier molecular orbitals, and density of states were carried out.
基于密度泛函理论（DFT），我们从多个角度分析了FOX-7分子在外部电场（EEF）作用下的变化，包括分子结构、电子结构、分解机理、前线分子轨道（FMO）和态密度（DOS）。结果表明，随着正EEF强度的增加，FOX-7分子的爆轰性能显著增强，同时其热稳定性也得到提高。这一发现挑战了传统观念，即炸药在外部电场下本质上是危险的，并为相关领域的研究提供了新的见解。为了进一步探究EEF对FOX-7热稳定性的影响，我们对EEF影响分解过程的机理进行了深入分析。我们的研究结果表明，施加正EEF显著增加了克服分子内氢转移和C-NO键断裂所需的能量，而对硝基异构化过程的影响相对较小。这一观察结果进一步表明，适当施加正EEF可以提高FOX-7的爆轰性能，而不会损害其热稳定性。进一步的研究表明，随着正EEF强度的增加，硝基的电负性逐渐增强，导致其中氧原子的电负性增加。这使得氧原子更易于参与化学反应。这一现象也解释了为什么随着正EEF强度的增加，FOX-7中硝基异构化所需的能垒逐渐降低。
基于密度泛函理论（DFT），在B3LYP/6-311G(d, p)水平下，分别在施加EEF和不施加EEF的情况下进行结构优化。所有优化结果均收敛且无虚频。基于优化后的结构，在B3LYP/def2-TZVPP水平上进一步进行单点能量计算。随后，对分子结构、电子结构、分解机理、前线分子轨道和态密度进行了分析。
