Pressure effects on structural, electronic, absorption, and thermodynamic properties of crystalline 2,4,6-triamino-3,5-dinitropyridine-1-oxide: A DFT study

Density functional theory calculations have been performed to study the structural, electronic, absorption, and thermodynamic properties of crystalline 2,4,6-triamino-3,5-dinitropyridine-1-oxide (TANPyo) in the pressure range of 0-50 GPa. The variation trends of the lattice constants, bond lengths, bond angles, intramolecular H-bonds, and dihedral angles under compression show that there are two structural transformations at 17 and 38 GPa, respectively. The remarkable changes in the bond lengths indicate that there are two possible initiation decomposition mechanisms of TANPyo under compression. As the pressure increases, the intramolecular H-bond strengthens. The obvious changes of the dihedral angles show that the planar structure of the TANPyo molecule is damaged under compression. Its absorption spectra show that as the pressure increases, the absorption coefficient of the N-H stretching decreases, while that of the O-H stretching increases. TANPyo has relatively high optical activity at high pressure. An analysis of thermodynamic properties indicates that both two structural transformations are endothermic and not spontaneous at room temperature. Copyright (c) 2013 John Wiley & Sons, Ltd.