材料的结构与性质是凝聚物理学、材料科学、化学等相关领域非常关注的基础问题之一。深入研究物质的微观结构不但有助于我们改善材料的性能而且能够指导我们发展新材料。含能材料在现代国防和民用经济建设中占据重要地位。虽然人类利用含能材料已有数百年历史，但对于其微观结构的稳定性和能量释放机理的研究还相对缺乏。特别是从微观层次认识含能炸药的起爆机理一直是现代爆轰物理、兵器科学、高压凝聚态物理、材料科学等多学科领域共同关注的重要科学问题。含能炸药在点火起爆过程中涉及高温高压环境，经历着复杂的物理、化学变化过程。但从根本上来说，材料的物理和化学性质与其结构息息相关，而研究含能材料在各种加载条件下发生爆炸的微观机理就是要揭示其分子在极端条件下如何发生结构转变或分解反应的问题。另外，研究压力作用下含能材料的分子结构变化对于认识其在起爆过程中的早期反应途径非常有益。因此，开展高压下含能材料的结构及稳定性研究对理解其分解和点火起爆等微观机理方面具有重要的科学意义。基于上述问题，本文采用金刚石压砧（DAC）和轻气炮加载技术，结合原位拉曼光谱技术、冲击热辐射技术以及第一性原理计算方法对几种典型含能材料在高压条件下的结构稳定性进行了研究，具体内容为：
首先，研究了硝基苯（NB）在高压下的结构稳定性。硝基苯作为一种结构最为简单的芳香硝基化合物，通常被作为研究硝基苯胺类炸药的模型物质。采用DAC 技术和原位拉曼光谱技术，在0-10 GPa压力范围内考察了硝基苯晶体的高压结构与分子振动特性。实验发现，在5 GPa压力附近硝基苯发生了一次结构的突变。为了深入理解实验观测结果，采用基于密度泛函理论（DFT）的第一性原理计算方法对硝基苯在高压下的结构响应行为进行理论模拟研究，计算发现分子键长、键角、二面角等物理参量均在7 GPa压力下发生一个不连续的跳变，预示着硝基苯在高压下发生了结构转变。对照实验和计算结果，我们认为硝基苯分子结构的变化是由于持续增加的压力促使其分子结构扭曲以抵抗增加的相互作用力，继而导致分子结构发生调整；高压下硝基苯拉曼光谱中有限的振动模式发生变化正是由于该分子结构的调整所致。
其次，研究了典型的含能材料硝基甲烷（NM）在冲击高压条件下的结构及其稳定性。从微观层面认识含能材料的冲击起爆机理是现代爆轰物理、高压凝聚态物理等多学科领域关注的重要问题之一。我们选取硝基甲烷这一结构最为简单的硝基化合物作为研究对象，基于轻气炮加载平台结合瞬态拉曼散射技术和冲击热辐射原位测量技术，研究了液态炸药硝基甲烷的拉曼特征峰随冲击压力的变化规律和冲击起爆延迟时间。实验结果表明，在冲击起爆前硝基甲烷仍然保持其光学透明特征。获得了硝基甲烷在冲击诱导期间生成新产物的拉曼光谱。首次发现在冲击高压下C-H键率先断裂的实验证据；新的实验结果为研究其他含能材料的点火反应以及冲击起爆机理提供了参考数据。
再者，研究了含能晶体1,3-二氨基-2,4,6-三硝基苯（DATB）在高压条件下的结构变化及其稳定性。DATB是硝基苯胺类炸药中一种重要的含能材料，与著名的高钝感炸药TATB的分子结构非常类似，但对其在不同压力下结构及性质的相关研究十分有限。本文采用色散修正密度泛函理论（DFT-D）计算方法，在0-15 GPa压力范围内对DATB晶体的结构及其稳定性进行了研究。结果表明，在常压条件下模拟计算的晶体常数、分子几何结构以及分子间相互作用特征均与实验结果吻合。其次，晶格常数、分子几何结构和弹性常数随压力的变化趋势均在7.5 GPa压力附近发生突变；根据晶体稳定性的力学判据，发现DATB晶体在7.3 GPa左右已不稳定，表明在7.5 GPa压力附近DATB晶体发生了结构失稳。
最后，研究了新型含能化合物3,4-二氨基-1,2,4三唑-1-氨基四唑-5-酮（ATO˙ DATr）在不同压力下的结构稳定性。ATO˙DATr具有较高的密度、良好的爆压和爆速，被认为是潜在的钝感含能材料。这类富氮含能化合物由于具有较高的氮元素和生成热，且产物主要是环境友好的氮气等优点而备受关注。本文采用DFT-D计算方法，在0-50 GPa 压力范围内研究了ATO˙ DATr的晶体结构、状态方程以及电子性质；同时，运用Hirshfeld表面和二维指纹图方法考察了其晶体内分子间相互作用的变化。结果表明，在零压下计算的晶格常数、分子几何结构以及分子间相互作用与实验值相一致。晶体的可压缩性呈现出各向异性并随着压力的增加而减小，ATO˙DATr的体积模量也比其他常见含能材料的要高；同时随着压力的增加晶体中的短程相互作用增强，涉及长程相互作用的de值减小，揭示出高压下ATO˙DATr晶体可压缩性的减小与分子间相互作用的增强有关。
 

Understanding of the relationship between the properties and structures of materials is an important topic in the fields of physics, material science and chemistry. Study substance microstructure is helpful to promote performance and synthesize the new materials. Although the energetic material is widely used for many years in the areas of military and civil engineering, the study on the microstructral stability and energy liberation mechanism is relatively limited. In particular, building a detailed molecular mechanism of the detonation is a common concern in the fields of modern detonation physics, weapon science and high pressure condensed matter physics. The detonation involves complex pressure and temperature condition, and experiences a complicated process of chemical and physical change. In another words, the nature of detonation mechanism is to reveal the structural transform or decomposition reaction of the explosives under extreme conditions. Thus, studies of the pressure effects on the structure response are important for understanding and modeling energetic materials. Moreover, a good knowledge of pressure-induced structural change is useful to understand the earlier stage reaction of the explosive. Therefore, investigations of the structural stability of the energetic materials under high pressure are important to establish a satisfied molecular mechanism of detonation. Based on the above considerations, the Diamond Anvil Cell (DAC), two-stage light –gas gun, Raman spectral measurement and DFT calculation were employed to study the structural stability of the typical energetic materials, including nitromthane (NM), nitrobenzene (NB), 1,3-Diamino-2,4,6-trinitrobenzene (DATB) and nitrogen-rich energetic compound 3,4-diamino-1,2,4-triazolium1-aminotetrazol-5-oneate (ATO˙DATr). Specific contents are as follows:
Firstly, we conduct the structural stability of nitrobenzene under high pressure. As a simplest structure of the aromatic nitro compounds, nitrobenzene is investigated as a model for understanding structural properties in nitro derivatives of benzene and anilines. Using the Raman spectroscopic technique, the high-pressure structure and vibrational modes of solid NB are examined under hydrostatic compression up to 10 GPa. The Raman spectra suggest that a subtle structural alteration occurred around 5 GPa. Also, to get further insight into the high-pressure Raman spectral changes, the dispersion corrected density functional theory (DFT-D) calculations are performed to exam pressure effects on the molecular geometry. The calculated data show a distinct change in the bond lengths, bond angles and dihedral angles around 7 GPa, indicating a structural change is occuring. Combining experimental and calculated results, suggest that NB molecules are distorted, and molecular structure is readjusted when the conformational change take place under high-pressure.
Secondly, we study the structural stability of nitromethane under shock-compression conditions. So far, understanding the reaction and detonation mechanism of energetic materials remain a difficult problem, and people put a great deal of time and effort into that. Nitromethane, the simplest nitro compound, is employed to exam the structural response to shock-compression of the energetic materials. Combine two-stage light-gas gun with Raman spectroscopy and thermal radiation measurements, we obtained the Raman spectrum and ignition delay time of liquid nitromethane under shocked-compression conditions. The experimental results indicate that the sample nitromethane is still transparent before the detonation occuring. In addition, Raman acteristic peaks of possible reaction products are observed for the first time. It is suggested that the C-H bond is early destructed under shock compression process, according to the assigned vibrational modes of the products. These interesting results also provide new insight into study of the initiation reaction and detonation mechanism of other energetic materials.
Thirdly, we determine the structural change and stability of DATB. DATB is a well-known explosive of the nitro derivatives of benzene and anilines, which molecular structure was similar to the famous insensitive explosive TATB. However, the structural information is poorly understood under high-pressure, especially the pressure-induced structural transformation remains an opening problem. Dispersion corrected density functional theory (DFT-D) calculation is performed to examine the structural response of DATB in the pressure range of 0-15 GPa. The calculated results of the crystal structure, molecular geometry and intermolecular close contacts are in good agreement with the experimental data at ambient pressure. To get further insight into the structural response to pressure of DATB, the crystal structure, elastic constants and mechanical stability of DATB are also studied under high pressure. The calculation results show that the pressure depenced of the lattice constants, molecular geometry and elastic constants are remarkably changed around 7.5 GPa. In addition, the elastic constants of DATB are not satisfied the mechanical stability criteria at 7.3 GPa, indicating that the DATB crystal structure is unstable.
Finally, we investigate the pressure effect on the crystalline structural stability of ATO˙DATr. The nitrogen-rich energetic compound ATO˙DATr is considered as an insensitive potential explosive due to its good detonation velocity and excellent detonation pressure. The kind of nitrogen-rich energetic compounds have been has attracted greater attention from scholars both at home and abroad because of their high heat of formation and nitrogen content as well as detonation products are environment friendly. To get further insight into the high-pressure behavior of these nitrogen-rich energetic compounds, the dispersion corrected density functional theory calculations are employed to study the crystal structure and molecular geometry. In addition, the intermolecular interactions including hydrogen bonds are examined by the Hirshfeld surfaces and two-dimensional fingerprint plots. These calculated results are in good agreement with the available experimental values. To gain insight into the pressure effect on crystal ATO˙DATr, we further study the lattice parameters, equations of state and electronic band gap under hydrostatic pressure from 0 to 50 GPa. Moreover, the variations of Hirshfeld surfaces and corresponding fingerprint plots with pressure are determined. Subsequently, the effects of hydrostatic compression on ATO˙DATr are dertemined. It is found that ATO˙DATr exhibits anisotropic compressibility. The calculated bulk modulus of ATO˙DATr is higher than other known energetic materials. Moreover, the number of closer contacts increased under pressure, while the overall shortening of these longer contacts is related to decrease of the maximum value de. The results shown above suggest that the decreased compressibility is related to the increased intermolecular interactions of ATO˙DATr under high pressure.