Low-temperature dependence on the THz spectrum of CL-20/TNT energetic cocrystal by molecular dynamics simulations

Based on the unique advantages of terahertz (THz) spectrum on the detection of energetic cocrystals, the low-temperature dependent THz spectra of CL-20/TNT cocrystal were investigated by using molecular dynamics (MD) simulations from 5 to 296 K, as well as three different crystal faces, (001), (120), and (010). When the temperature decreases below 95 K, we have observed two new peaks for CL-20/TNT cocrystal, at 4.58 and 5.99 THz, respectively. Also, the THz peaks below 1.5 THz gradually disappear under cooling from 296 to 5 K, and they should originate from the lattice thermal vibrations. THz absorption peaks of CL-20/TNT cocrystal reveal frequency shifting, linearly dependent on temperature. Four of them are red shift and other two are blue shift of THz vibrational peaks of CL-20/TNT cocrystal with the temperature increase. The frequency shifts can be attributed to the effects of lattice thermal expansion on inter-/intramolecular vibrational modes as well as their coupling. From the temperature-dependent THz spectra of different crystal faces, we further confirm the response of different kinds of intermolecular interactions on the THz spectrum of CL-20/TNT cocrystal.