Charge Density Distribution, Electrostatic Properties and Sensitivity of the Highly Energetic Molecule 2,4,6-Trinitro-1,3,5-triazine: A Theoretical Study

Ab initio and density functional theory (DFT) calculations were carried out on the energetic propellant molecule 2,4,6-trinitro-1,3,5-triazine (TNTA) to understand its bond topology and its energetic properties using the theory of atoms in molecules (AIM). The DFT method predicts that the electron density ρbcp(r) at the bond critical points of ring C–N bonds is ~2.34 eÅ-3 and the corresponding Laplacian ∇ρbcp(r) is ~ -24.4 eÅ-5; whereas these values are found to be very small in the −NO2 group attached to C–N bonds [ρbcp(r): ~1.73 eÅ-3 and ∇ρbcp(r): ~ -14.5 eÅ-5]. The negative Laplacian values of C–NO2 bonds are significantly lower which indicates that the charges of these bonds are highly depleted. The C–NO2 bonds exhibit low bond order (~0.8), as well as low (~56.4 kcal/mol) bond dissociation energy. As we reported in our earlier studies, we found high bond charge depletion for these bonds, which are considered the weakest bonds in the molecule. The frontier orbital energies exhibit a wide band gap, which is larger than those of existing molecules TATB, TNT and TNB. The impact sensitivity (H50%) (4.2 m) and oxygen balance (2.77%) were calculated and compared with related structures. Large negative electrostatic potential regions were found near the nitro groups where reaction is expected to occur. The relation between charge depletion ∇ρbcp(r) and the electrostatic potential at the bond midpoints Vmid reveals the sensitive areas of the molecule.