Bond and Band Engineering Group, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu 610031, People's Republic of China.
Bond and Band Engineering Group, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu 610031, People's Republic of China.
Spectrochim Acta A Mol Biomol Spectrosc. 2023 May 15;293:122489. doi: 10.1016/j.saa.2023.122489. Epub 2023 Feb 15.
FOX-7 (1,1-diamino-2,2-dinitroethene) as one of the widely studied insensitive high explosives exists five polymorphs (α, β, γ, α', ε) whose crystal structures have been determined by XRD (X-rays Diffraction) and which are investigated by a density functional theory (DFT) approach in this work. The calculation results show that the GGA PBE-D2 method can reproduce the experimental crystal structure of FOX-7 polymorphs better. The calculated Raman spectra of FOX-7 polymorphs were compared in detail and fully with the experimental Raman spectra data and it was found that the calculated Raman spectra frequencies have an overall red-shift in middle band (800-1700 cm), and that the maximum deviation does not exceed 4 % (The maximum point is the mode of CC in plane bending). The high-temperature phase transform path (α → β → γ) and the high-pressure phase transform path (α → α'→ε) can be well represented in the computational Raman spectra. In addition, crystal structure of ε-FOX-7 was performed up to 70 GPa to probe Raman spectra and vibrational properties. The results showed that the NH Raman shift is jittering with pressure (not smooth compared to other vibrational modes) and NH anti-symmetry-stretching appears red-shifted. The vibration of hydrogen mixes in all of other vibrational modes. This work shows that the dispersion-corrected GGA PBE method can reproduce the experimental structure, vibrational properties and Raman spectra very well.
FOX-7（1,1-二氨基-2,2-二硝基乙烯）是广泛研究的钝感高能炸药之一，存在五种多晶型体（α、β、γ、α'、ε），其晶体结构已通过 X 射线衍射（XRD）确定，并在这项工作中通过密度泛函理论（DFT）方法进行了研究。计算结果表明，GGA PBE-D2 方法可以更好地再现 FOX-7 多晶型体的实验晶体结构。详细比较并与实验拉曼光谱数据完全比较了 FOX-7 多晶型体的计算拉曼光谱，并发现计算的拉曼光谱频率在中间带（800-1700 cm）整体红移，最大偏差不超过 4%（最大值是 CC 面内弯曲模式）。可以在计算的拉曼光谱中很好地表示高温相转变路径（α→β→γ）和高压相转变路径（α→α'→ε）。此外，对ε-FOX-7 的晶体结构进行了高达 70 GPa 的探测以研究拉曼光谱和振动特性。结果表明，NH 拉曼位移随压力而抖动（与其他振动模式相比不光滑），NH 反对称伸缩出现红移。氢的振动混合在所有其他振动模式中。这项工作表明，经色散校正的 GGA PBE 方法可以很好地再现实验结构、振动特性和拉曼光谱。
