DFT studies on the four polymorphs of crystalline CL-20 and the influences of hydrostatic pressure on epsilon-CL-20 crystal.
DFT studies on the four polymorphs of crystalline CL-20 and the influences of hydrostatic pressure on epsilon-CL-20 crystal.
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DOI：
10.1021/jp066833e
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发表时间：
2007-02
期刊：
影响因子：
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通讯作者：
Xiao-Juan Xu;Weihua Zhu;Heming Xiao
中科院分区：
文献类型：
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作者：
Xiao-Juan Xu;Weihua Zhu;Heming Xiao
基于密度泛函理论 (DFT)，采用广义梯度近似 (GGA) 的四种不同方法来研究 CL-20 的四种多晶型物（α.H2O、β、γ 和 epsilon 相）的结构和电子特性，CL-20 是一种著名的高能量密度化合物 (HEDC)。松弛的晶体结构与实验数据吻合良好。根据前沿能带的构成和Mulliken布居分析，预测N-NO2键是热解过程中的触发键。 α-CL-20.H2O 的态密度 (DOS) 与其他三种晶体的态密度有所不同，因为它包含贡献前沿能带的 H2O 分子。四种不同方法得到的带隙是一致的。根据带隙计算值，预测CL-20四种多晶型物的灵敏度为epsilon < beta < gamma < alpha.H2O，与实验结果吻合较好。还使用 GGA-PBE 方法在 0-400 GPa 的压力范围内研究了静水压缩对最稳定的 epsilon-CL-20 的影响。 epsilon-CL-20 在低压或高压下具有各向异性压缩性。发现带隙随着压力的增加而减小，显示出相应的灵敏度增加。根据带隙和DOS随压力的变化，400 GPa被认为是绝缘体-金属相变的临界压力。
Based on density functional theory (DFT), four different methods with the generalized gradient approximation (GGA) have been employed to investigate the structural and electronic properties of the four polymorphs (alpha.H2O, beta, gamma, and epsilon phases) of CL-20, which is a well-known high energy density compound (HEDC). The relaxed crystal structures compare well with experimental data. According to the constitution of the frontier energy bands and the Mulliken population analyses, the N-NO2 bond is predicted to be the trigger bond during thermolysis. The density of states (DOS) of alpha-CL-20.H2O is somewhat different from those of the other three crystals for its inclusion of H2O molecules that contribute the frontier energy bands. The band gaps obtained from the four different methods are consistent with each other. According to the calculated values of band gaps, the sensitivity of the four polymorphs of CL-20 is predicted as epsilon < beta < gamma < alpha.H2O, which agrees well with the experimental result. The effects of hydrostatic compression on the most stable epsilon-CL-20 have also been investigated using the GGA-PBE method in the pressure range of 0-400 GPa. epsilon-CL-20 has anisotropic compressibility at low or high pressure. The band gap is found to decrease with increasing pressure, showing the corresponding sensitivity increase. Based on the changes of the band gap and DOS with pressure, 400 GPa is considered to be the critical pressure for the insulator-metal phase transition.