HIGH PRESSURE BEHAVIOR OF CRYSTALLINE DIHYDROXYLAMMONIUM 5,5'-BISTETRAZOLE-1,1'-DIOLATE: FIRST-PRINCIPLES STUDY

Density functional theory (DFT) periodic calculations were performed to study the geometrical and electronic structures of energetic compound dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50) under the pressure ranging from 0 to 400 GPa. The optimized crystal structure by the local density approximation (LDA) with CA-PZ functional matches well with the experimental values under the ambient pressure. When the structural transformations occur under the pressure of 126, 288, and 334 GPa, with the pressure increasing, the lattice constants, unit cell volume, total energy, interatomic distances, bond angles, atomic charges, and bond populations of TKX-50 change gradually. First of all, TKX-50 is rearranged in the crystal and the improvement of the molecular planarity occurs. Next, structural transformation appears with the distortion of the tetrazole rings. Finally, the rotation of molecular conformation occurs. The results of the band gap and density of states show that TKX-50 crystal, with the increase of pressure, undergoes an electronic transition from the semiconductor to the metallic system. These results provide basic information for the high pressure behavior of crystalline TKX-50.