RDX Compression, α→ γ Phase Transition, and Shock Hugoniot Calculations from Density-Functional-Theory-Based Molecular Dynamics Simulations,The Journal of Physical Chemistry C

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RDX Compression, α→ γ Phase Transition, and Shock Hugoniot Calculations from Density-Functional-Theory-Based Molecular Dynamics Simulations
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2016-08-26 00:00:00 , DOI: 10.1021/acs.jpcc.6b06415
Dan C. Sorescu ₁ , Betsy M. Rice ₂

Affiliation

Prediction of the density and lattice compression properties of the α and γ phases of the hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX) crystal and of the low-pressure α → γ phase transition upon pressure increase are general tests used to assess the accuracy of density-functional-theory- (DFT-) based computational methods and to identify the essential parameters that govern the behavior of this high-energy-density material under extreme conditions. The majority of previous DFT studies have analyzed such issues under static optimization conditions by neglecting the corresponding temperature effects. In this study, we extend previous investigations and analyze the performance of dispersion-corrected density functional theory to predict the compression of RDX in the pressure range of 0–9 GPa and the corresponding α → γ phase transition under realistic temperature and pressure conditions. We demonstrate that, by using static dispersion-corrected density functional theory calculations, direct interconversion between the α and γ phases upon compression is not observed. This limitation can be addressed by using isobaric–isothermal molecular dynamic simulations in conjunction with DFT-D2-calculated potentials, an approach that is shown to provide an accurate description of both the crystallographic RDX lattice parameters and the dynamical effects associated with the α→ γ phase transformation. An even more comprehensive and demanding analysis was done by predicting the corresponding shock Hugoniot curve of RDX in the pressure range of 0–9 GPa. It was found that the theoretical results reproduce reasonably well the available experimental Hugoniot shock data for both the α and γ phases. The results obtained demonstrate that a satisfactory prediction of the shock properties in high-energy-density materials undergoing crystallographic and configurational transformations is possible through the combined use of molecular dynamics simulations in the isobaric–isothermal ensemble with dispersion-corrected density functional theory methods.

中文翻译：

基于密度泛函理论的分子动力学模拟进行RDX压缩，α→γ相变和冲击休克体计算

六氢-1,3,5-三硝基-1,3,5- s的α和γ相的密度和晶格压缩特性的预测-三嗪（RDX）晶体和压力增加时的低压α→γ相变是用于评估基于密度泛函理论（DFT-）的计算方法的准确性并确定支配着这些基本参数的常规测试这种高能量密度材料在极端条件下的行为。以前的大多数DFT研究都忽略了相应的温度效应，从而在静态优化条件下分析了此类问题。在这项研究中，我们扩展了以前的研究并分析了色散校正密度泛函理论的性能，以预测在实际温度和压力条件下，RDX在0–9 GPa压力范围内的压缩以及相应的α→γ相变。我们证明，通过使用静态色散校正的密度泛函理论计算，未观察到压缩时α和γ相之间的直接相互转换。可以通过将等压-等温分子动力学模拟与DFT-D2计算的电势结合使用来解决这一局限性，该方法显示出可以精确描述晶体学RDX晶格参数以及与α→γ相关的动力学效应相变。通过预测RDX在0–9 GPa压力范围内的相应休克尼奥特曲线，可以进行更加全面和苛刻的分析。结果发现，理论结果可以很好地重现α和γ相的Hugoniot冲击实验数据。

更新日期：2016-08-26

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