Miao M S, Dreger Z A, Winey J M, Gupta Y M
Institute for Shock Physics and Department of Physics, Washington State University, Pullman, Washington 99164-2816, USA.
J Phys Chem A. 2008 Nov 27;112(47):12228-34. doi: 10.1021/jp807285u.
Pressure effects on the vibrational structure of alpha-RDX were examined using density functional theory (DFT) up to 4 GPa. The calculated vibrational frequencies at ambient conditions are in better agreement with experimental data than are previous single molecule calculations. The calculations showed the following pressure-induced changes: (i) larger shifts for lattice modes and for internal modes associated with the CH(2) and NO(2) groups as compared to the pressure shifts for modes associated with the triazine ring, (ii) enhancement of mixing between different vibrations, for example, between NN stretching and CH(2) scissor, wagging, twisting vibrations, and (iii) increase in mixing between translational lattice vibrations and the NO(2) wagging vibrations, reducing the distinction between internal and lattice modes. The calculated volume and lattice constants at ambient pressure are larger than the experimental values, due to the inability of the present density functional approach to correctly account for van der Waals forces. Consequently, the pressure-induced frequency shifts of many modes deviate substantially from experimental data for pressures below 1 GPa. With increasing pressure, both the lattice constants and the frequency shifts agree more closely with experimental values.
使用密度泛函理论（DFT）研究了高达4 GPa压力对α-黑索今振动结构的影响。与之前的单分子计算相比，在环境条件下计算得到的振动频率与实验数据吻合得更好。计算结果显示了以下压力诱导变化：（i）与三嗪环相关模式的压力位移相比，晶格模式以及与CH(2)和NO(2)基团相关的内模式有更大的位移；（ii）不同振动之间的混合增强，例如，NN伸缩振动与CH(2)剪式振动、摇摆振动和扭曲振动之间；（iii）平移晶格振动与NO(2)摇摆振动之间的混合增加，减少了内模式和晶格模式之间的区别。由于目前的密度泛函方法无法正确考虑范德华力，在环境压力下计算得到的体积和晶格常数大于实验值。因此，对于低于1 GPa的压力，许多模式的压力诱导频率位移与实验数据有很大偏差。随着压力增加，晶格常数和频率位移都与实验值更接近。
