几种多态含能材料构型转变的DFT研究

DFT Study on the Configuration Transformation of Several Polymorphic Energetic Materials

为了从分子层面上对含能材料不同分子构型间的转变情况有一个直观认识,借助Gaussian 09软件,运用密度泛函理论(DFT),采用TS算法搜寻β-RDX→α-RDX、γ-HMX→β-HMX、ε-CL-20→β-CL-20及β-FOX-7→α-FOX-7在分子构型转变过程中的过渡态结构,确定了它们的构型转变过程;并通过计算吉布斯自由能随构型转变路径的变化,比较多态含能材料分子构型转变的难易程度。结果表明,由亚稳晶型到稳定晶型的转变首先会越过过渡态,克服自由能能垒转变为亚稳态结构,实现β-RDX→α-RDX、γ-HMX→β-HMX、ε-CL-20→β-CL-20及β-FOX-7→α-FOX-7分子构型转变分别需要克服的自由能能垒分别为5.25、22.21、9.69和10.24kJ/mol。因此,常温常压下β-RDX→α-RDX、γ-HMX→β-HMX、ε-CL-20→β-CL-20及β-FOX-7→α-FOX-7构型转变的难度大小排序为:HMX>>FOX-7>CL-20>RDX。

In order to have an intuitive understanding of the transition in different molecular configurations of energetic materials at the molecular level the transition state structures of β-RDX→α-RDX,γ-HMX→β-HMX,ε-CL-20→β-CL-20 and β-FOX-7→α-FOX-7 during molecular configuration transformation were searched by Gaussian 09 software with density functional theory(DFT) and TS algorithm,and their conformational transformation processes were determined. The difficulty of molecular configuration transition of polymorphic energetic materials was estimated by calculating the change of Gibbs free energy along the configuration transition path. The results show that the transition from the metastable crystal form to the stable crystal form will first cross the transition state and overcome the free energy barrier to transform into a metastable state structure. The free energy barriers to be overcome for the β-RDX→α-RDX, γ-HMX→β-HMX, ε-CL-20→β-CL-20 and β-FOX-7→α-FOX-7 molecular configuration transitions were 5.25, 22.21, 9.69 and 10.24 kJ/mol, respectively. Therefore, the difficulty level of transformations for β-RDX→α-RDX, γ-HMX→β-HMX, ε-CL-20→ β-CL-20 and β-FOX-7→α-FOX-7 under normal temperature and pressure is HMX>>FOX-7>CL-20>RDX.