Pressure-induced phase transitions and mechanical properties of insensitive high explosive 1,1-diamino-2,2-dinitroethylene

The structural and mechanical properties of an insensitive high-explosive 1,1-diamino-2,2-dinitroethylene (FOX-7) polymorphs were studied using dispersion-corrected density functional theory calculations. The predicted lattice parameters of FOX-7 polymorphs agree well with the available single-crystal X-ray diffraction data. From our elastic modulus calculations, we found that the epsilon phase has the highest shear modulus G, Young's modulus E, longitudinal speed C-L, and shear speed C-S, respectively. Moreover, both alpha and alpha ' phase are brittle, epsilon phase is ductile nature. The results of Hirshfeld surfaces and fingerprint plots indicate that the alpha and alpha ' phase possess similar molecular packing modes. Meanwhile, the epsilon phase is found to have the strongest pi horizontal ellipsis pi interactions because of the nearly planer molecules formed a planar layer in the crystal. The pressure effects on the alpha and alpha ' phase presented an obvious anisotropy, a pressure-induced phase transition from phase alpha ' (P2(1)/n) to epsilon phase (P1) was studied. And we also analyze the influence of pressure on the electronic structure.