The heats of formation (HOF) for 49 tetrazole derivatives are calculated with the density functional theory (DFT) B3LYP method by means of designed isodemic and isogyric reactions. The average absolute deviation for five compounds for which the experimental HOFs are available is less than 2kcal/mol target accuracy of G-2 theory. It has been demonstrated that for compounds involving delocalized bonds, choosing molecules containing all of the delocalized bonds as reference compounds is an appropriate approach. The calculated HOFs indicate that most neutral 2H-isomers are more stable than the corresponding 1H-isomers whereas the 1-substituted tetrazolate anions are more stable than the corresponding 2-substituted ones. Furthermore, our results consistently show that C-substituted tetrazoles are more stable than the corresponding N substituted isomers. Our calculated heat of formation calls into question the experimental heat of formation of 2-methyltetrazole.

The molecular geometries, infrared vibrational spectra, and thermodynamic properties of octanitrocubane (ONC) are calculated using the density functional theory (DFT) method at the B3LYP/6-31G* level. The IR frequency scaling factor 0.9501 suitable for polynitrocubanes is obtained at the B3LYP/6-31G* level, and the calculated IR frequencies of ONC are scaled. The accurate heat of formation 726.47kJ/mol of ONC in gas phase is obtained via designed isodesmic reaction in which the cubane cage skeleton has been kept. The sublimation enthalpy, density, and heat of formation for ONC crystal are also calculated, and they are 220.63kJ/mol, 2.189g/cm3, and 505.84kJ/mol, respectively. In addition, the estimated detonation velocity and detonation pressure of ONC are 10.26mm/ms and 520.86kbar, respectively. Finally, the pyrolysis mechanism of ONC is studied using various theoretical methods, i.e., MP2, DFT, and selected MINDO/3 semiempirical MO, based on the unrestricted Hartree-Fock model. The calculated results show that the pyrolysis initiation reaction of ONC, i.e., rate-controlling step, is to form a diradical by the single C-C bond breaking in the cube. The second C-C bond breaking is easily followed to form a nitrocyclooctatetraene. The calculated activation energy for the pyrolysis initiation reaction of ONC, obtained from B3LYP/6-31G* method, is 155.30kJ/mol, which this rather large activation energy indicates that ONC is a new type of energetic material with less sensitivity and better thermal stability, and has highly exploitable values.

A reaction profile for the nitration of benzene with nitronium ion has been successfully calculated for the first time. Stationary points were located and characterized by the DFT procedures at the B3LYP/ 6-311G** level. When NO2 + approaches the benzene molecule, a weakly bound π-complex was first produced, in which the distances between the nitrogen atom of nitronium ion to both carbon atoms C1 and C6 of benzene ring were equal. This bifurcation point was characterized as a transition state leading to a σ-complex reactant by shifting the positive ion to either single carbon C1 or C6. The σ-complex reactant (σ-R) finally reaches to the Wheland intermediate (σ-INT) via a σ-complex transition state (σ-TS). The formation of the σ-TS is the rate-determining step, and the barrier height is 8.37 kJ/mol with the correction for ZPVE. A comparison of the intensities and the shifts given by the computational infrared C-N and C-H stretching frequencies on going from σ-TS to σ-INT shows that the formation of bond C1-N13 and the cleavage of bond C1-H12 are not concerted but stepwise in the process of the nitration. This agrees well with the experimental fact of the lack of kinetic isotopic effect in most aromatic nitration reactions.

The DFT/B3LYP method with different basis sets has been applied to the systems of (H2AlN3)n (n=1-4). (H2AlN3)2 is found to exhibit the planar Al2N2 ring structure and possesses D2h symmetry. The transition state for the monomer to dimer conversion is located, and the activation energy is presented. (H2AlN3)3 involving a six-membered Al3N3 ring is found to exhibit two minima with very similar binding energies (ca. -274 to -278 kJ