Uniaxial compression behavior and spectroscopic properties of energetic 1,1-diamino-2,2-dinitroethylene(FOX-7) crystals from density functional theory calculations

Using dispersion-corrected density functional theory (DFT),we investigate the effect of uniaxial compression on1,1-diamino-2,2-dinitroethene (FOX-7) crystal.Principal and shear stresses along the 100],010],and 001]orientations exhibit considerable anisotropic compressibility.Raman spectra are complemented by DFT calculations in vibrational modes.Several abnormal pressure-induced changes in selected Raman modes are observed along the 100] orientation.Combined Raman peak shifts with inter/intra-molecular hydrogen bonds and N-H/N-O covalent bonds,the results demonstrate that the spectroscopic variation are associated with the rearrangement of hydrogen-bonded networks of FOX-7 crystal.These findings imply a possible phase transformation or some minor changes in molecular conformation in the pressure regions under uniaxial compression.