Ab initio study of electronic structure and properties in crystalline 1,1,3,3,5,5-hexaazidocyclotriphosphazene

The banding and electronic structures of crystalline 1,1,3,3,5,5- hexaazidocyclotriphosphazene (P₃N₂₁) have been investigated at DFT-B3LYP/6-31G(d) level. Relaxed crystal structure compares well with experimental data. The energy gap is 5.57 eV, indicating that P ₃N₂₁ is an insulator. The frontier orbital is mainly formed by atomic orbitals of azido group, so it is the most reactive part of the molecule. The intermolecular interaction is strong along the direction that is nearly perpendicular to the phosphazene ring. The distribution of electrostatic potential is quite uneven, so P₃N₂₁ has a very high impact sensitivity. The point charge electrostatic potential is very high between the azido groups of the neighboring molecules, which indicates that the crystal lattice in this position may easily be broken and becomes the explosion center when P₃N₂₁ is impacted. The overlap populations of P-N_α bonds are much less than those of other bonds, therefore the P-N_α bonds first rupture by external stimuli, which agrees well with the experimental study of mass spectrum.