Averkiev Boris B, Dreger Zbigniew A, Chaudhuri Santanu
Institute for Shock Physics, Washington State University , Pullman, Washington 99164-2816, United States.
J Phys Chem A. 2014 Oct 30;118(43):10002-10. doi: 10.1021/jp508869n. Epub 2014 Oct 21.
Pressure effects on the Raman vibrations of an energetic crystal FOX-7 (1, 1-diamino-2, 2-dinitroethene) were examined using density functional theory (DFT) calculations. High accuracy calculations were performed with a periodic plane-wave DFT method using norm-conserving pseudopotentials. Different exchange-correlation functionals were examined for their applicability in describing the structural and vibrational experimental data. It is shown that the PBE functional with an empirical dispersion correction by Grimme, PBE-D method, reproduces best the molecular geometry, unit cell parameters, and vibrational frequencies. Assignments of intramolecular Raman active vibrations are provided. The calculated pressure dependence of Raman shifts for the intramolecular and lattice modes were found to be in good agreement with the experimental data; in particular, the calculations predicted correctly a decrease of frequencies for the NH2 stretching modes with pressure. Also, in accord with experiments, the calculations indicated some instances of modes mixing/coupling with increasing pressure. This work demonstrates that the dispersion-corrected PBE functional can account for the structural and vibrational properties of FOX-7 crystal at ambient and high pressures.
利用密度泛函理论（DFT）计算研究了压力对高能晶体FOX - 7（1,1 - 二氨基 - 2,2 - 二硝基乙烯）拉曼振动的影响。采用具有守恒规范赝势的周期性平面波DFT方法进行了高精度计算。研究了不同的交换相关泛函在描述结构和振动实验数据方面的适用性。结果表明，采用Grimme经验色散校正的PBE泛函，即PBE - D方法，能最好地再现分子几何结构、晶胞参数和振动频率。给出了分子内拉曼活性振动的归属。发现分子内和晶格模式的拉曼位移的计算压力依赖性与实验数据吻合良好；特别是，计算正确地预测了NH2伸缩模式的频率随压力降低。此外，与实验一致，计算表明随着压力增加存在一些模式混合/耦合的情况。这项工作表明，色散校正的PBE泛函可以解释FOX - 7晶体在常压和高压下的结构和振动性质。
