Revealing hydrogen-bond reorganization and band gap modulation in high-pressure DATB via first-principles Raman spectroscopy.

Understanding the high-pressure response of energetic materials is essential for controlling their sensitivity, performance, and safety. Using dispersion-corrected density functional theory and first-principles vibrational spectroscopy, we systematically investigate the structural evolution and electronic response of 1,3-diamino-2,4,6-trinitrobenzene (DATB) under compression. The vibrational spectra reveal that NH2 and NO2 internal modes change peak shape and intensity at 1.5 GPa and split at 7.5 GPa, while discontinuous frequency shifts of all lattice modes point to isostructural transitions at these pressures. These spectral signatures are traced to the pressure-induced reorganization of intra- and intermolecular hydrogen bonds and an abrupt change in the molecular stacking angle. The hydrogen-bond reorganization shifts the electronic states of carbon and amino nitrogen toward lower energies, driving an indirect-to-direct band gap transition at 1.5 GPa. At 7.5 GPa, both valence and conduction band edges shift to the G point, and the band gap widens by 0.28 eV. The results establish a direct coupling between pressure-driven vibrational instabilities, hydrogen-bond reorganization, and electronic structure modulation in energetic molecular crystals.