基于Voronoi动态光谱计算及信号解读的HMX温压相结构变化特性研究

Octogen (HMX) is the main energetic component of the commonly used high-explosive. HMX possesses several phase structures, which would complicatedly transform with each other under high temperature and pressure. The different phase structures of HMX have different crystal densities, sensitivities, and chemical decomposition pathways, directly affecting the dynamic response properties and detonation performance of the HMX-based high-explosive under external stimulation. Thus, it is necessary to systematically investigate the phase transition of explosive. However, the existing experimental techniques can not sufficiently interpret the detected signal, resulting in a lack of understanding of the microscopic physical mechanism of explosive phase transition. The establishment and application of the theory system of explosive phase transition are restricted. In this program, we will study the phase structure transformation and the features of Infrared, Raman spectra of HMX under different temperatures and pressures, basing on ab initio molecular dynamics (AIMD) combined with TRAVIS dynamic spectrum calculation method. The corresponding relationship between crystalline microscopic structures (chemical bonds, molecular configuration, intermolecular interaction, and so on) and spectrum signal (quantity, position, intensity, and shape) is explored. Basing on that, the existing experimental spectrum data is further analyzed to uncover the physical mechanism of explosive phase transition at atomic and molecular level.

奥克托今（HMX）是常用高能炸药的主要含能组分。HMX具有多种相结构，在高温高压下会发生复杂的相变。不同相结构具有不同的晶体密度、感度和化学分解路径，直接影响到以HMX为基的高能炸药在外界刺激下的动态响应特性和爆轰性能。因此，有必要系统研究炸药的相变问题。然而现有实验技术对检测信号的解读并不充分，导致学术界对炸药相变过程微观物理机制的认识还很缺乏。严重制约了炸药相变理论体系的建立及其在实际中的应用。本项目拟采用从头算分子动力学（AIMD）结合TRAVIS动态光谱计算方法，研究HMX在不同温度、压力下的相结构变化和红外、拉曼光谱特性。探索晶体结构(化学键、分子构型、分子间作用等)与光谱信号(数量、位置、强度、形状)的对应关系。在此基础上，进一步解读已有实验光谱数据，从原子分子尺度研究炸药相变的物理机制。

本项目基于从头算分子动力学(AIMD)方法，从原子分子尺度研究了HMX炸药的微观结构变化，揭示了其晶格常数、化学键、二面角、原子电荷分布随温度、压力的变化规律；并采用TRAVIS(TRajectory Analyzer and VISualizer)动态光谱计算方法和相应的光谱分解计算策略，得到了晶体体系和分子环、CH2、NO2、N-NO2等主要官能团的红外、拉曼振动光谱。通过微观结构和光谱对比分析，确定了300-500 K、0-40 GPa范围内典型的温压相变过程，建立了光谱信号与分子结构的对应关系。结果表明，HMX分子赤道方向C-N键和轴向N-N键的伸缩形变最明显，进而引起的分子环变形、N-NO2基团旋转是诱发晶体结构相变的主要原因。在温度相变中，轴向N-NO2基团在β→α的相变过程中起到主要作用；而赤道向N-NO2基团在β→δ的相变过程中表现更为突出。在压力相变中，基团间的关联作用在高压下明显增强，作为分子骨架的分子环参与了整个相变过程，是压力相变的重要载体。此外NO2基团形变对β→ζ的相变过程也起到了作用；轴向N-NO2基团形变是引起ζ→ε相变的又一重要因素。更高压力下的结构形变(如ε→φ、φ→η)，由N-NO2基团、CH2、分子环等基团共同作用引起。上述成果，不但为炸药相变实验光谱信号解读、相变过程物理认识提供了重要的理论支撑；更有利于深入理解炸药微观结构响应和点火反应机制，从而更准确、有效的评估其爆轰反应性能。