Pressure induced structural behavior of energetic cocrystal TNT/TNB: a density functional theory study

In order to find out the relationship between external pressures and properties of energetic materials, we used the density functional theory (DFT) method to investigate the structural, electronic, and absorption properties of crystalline 2,4,6-trinitrotoluene (TNT)/2,4,6-trinitrotoluene (TNB) under hydrostatic compression of 0-100 GPa. By analyzing the change of lattice constants (a, b, and c) of TNT/TNB under compression conditions, we found that variation tendency of the lattice constants was anisotropic. The b-axis is much stiffer than that along the a- and c-axes, which indicates that the TNT/TNB crystal is anisotropic within a certain pressure region. The pressure-induced structure transformation results in the new covalent bonds O11-C13, O12-C11, O8-C4, and O1-C12 at 60 GPa, and O4-C5 at 80 GPa, respectively. By analyzing the band structure and density of states of TNT/TNB in the pressure range over 40 GPa, the electronic structure of TNT/TNB changed to metallic system, which indicated it becomes more sensitivity under high pressures. The pressure-induced structure transformation of TNT/TNB also contributed to the relatively high optical activity of TNT/TNB at 70 GPa.