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 ϵ phase has the highest shear modulus G, Young's modulus E, longitudinal speed CL, and shear speed CS, respectively. Moreover, both α and α′ phase are brittle, ϵ phase is ductile nature. The results of Hirshfeld surfaces and fingerprint plots indicate that the α and α′ phase possess similar molecular packing modes. Meanwhile, the ϵ phase is found to have the strongest π...πinteractions because of the nearly planer molecules formed a planar layer in the crystal. The pressure effects on the α and α′ phase presented an obvious anisotropy, a pressure-induced phase transition from phase α′ (P21/n) to ϵ phase (P1) was studied. And we also analyze the influence of pressure on the electronic structure.