Pressure-induced structural, vibrational and electronic evolution of ε-CL-20:A periodic DFT study

The structures, IR and Raman spectra, electronic and optical properties of ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-CL-20) crystal under 0-250 GPa have been systematically studied by periodic density functional theory (DFT) method. The crystal structure, molecular configuration and hydrogen bond are discontinuous at 195 GPa, which indicate that the structural mutation of ε-CL-20 occurs. IR and Raman analysis prove that the structure of ε-CL-20 do mutate, and high pressure makes the system appear more absorption peaks of C-H stretching in the high frequency region of more than 3000 cm^-1. The calculation of electronic properties show that the band gap decreases with the increase of pressure, and the valence band maxima (VBM) and conduction band minima (CBM) mainly come from the contribution of O and N atoms, indicating that N-NO₂ group is the active center of ε-CL-20. High pressure broadens the absorption peak and increases the absorption coefficient, which means that the optical absorption activity of the system increases. This study provides a theoretical basis for the high pressure behavior of energetic materials.