In recent years, there has been a considerable interest in developing high oxygen compounds as oxidizers for, for example, composite explosives. 2,2,3,3-Tetranitroaziridine (TNAD) is a new designed compound with high oxygen balance (25.11%) and is environmentally friendly. A synthesis route of TNAD was suggested in this study, and the thermodynamic possibilities of reactions were evaluated by the changes in the free energy obtained with the density functional theory (DFT). The strong strain energy (E_s = 292.28 kJ/mol) of TNAD leads the C–C bond in the ring more fragile than the C–NO₂ bond, and the activation energy (E_a) of pyrolysis of the C–C bond (119.14 kJ/mol at the B3LYP/6-31G* level of DFT) is higher than that of 2,4,6-trinitrotoluene (TNT) (113.00 kJ/mol). The topological analysis with the contour maps of electron density was used to show the changes of the electron density at the critical points (BCP) in the process of homolysis of the C–C bond. In addition, the energy gap between the frontier orbitals of TNAD (ΔE_g = 5.22 eV) is slightly higher than that of 1,3,3-trinitroazetidine (TNAZ, 5.06 eV). And the HOMO LUMO transition plays important roles in the UV spectrum. The noncovalent interactions in the TNAD/RDX composite were estimated to be stronger than that in TNAZ/RDX, that is, the former may have better compatibility than the latter. TNAD/RDX with the weight ratio of w_TNAD/w_RDX = 0.46/0.54 has the wonderful performance (D = 9.14 km/s, P = 37.30 GPa, and I_s = 285.47 s) which is better than that (D = 8.85 km/s, P = 35.09 GPa, and I_s = 272.33 s) of TNAZ/RDX with the same weight ratio. Copyright © 2014 John Wiley & Sons, Ltd.

Nitrogen-rich heterocyclic bases and oxygen-rich acids react to produce energetic salts with potential application in the field of composite explosives and propellants. In this study, 12 salts formed by the reaction of the bases 4-amino-1,2,4-trizole (A), 1-amino-1,2,4-trizole (B), and 5-aminotetrazole (C), upon reaction with the acids HNO₃ (I), HN(NO₂)₂ (II), HClO₄ (III), and HC(NO₂)₃ (IV), are studied using DFT calculations at the B97-D/6-311++G** level of theory. For the reactions with the same base, those of HClO₄ are the most exothermic and spontaneous, and the most negative Δ_rG_m in the formation reaction also corresponds to the highest decomposition temperature of the resulting salt. The ability of anions and cations to form hydrogen bonds decreases in the order NO₃⁻>N(NO₂)₂⁻>ClO₄⁻>C(NO₂)₃⁻, and C⁺>B⁺>A⁺. In particular, those different cation abilities are mainly due to their different conformations and charge distributions. For the salts with the same anion, the larger total hydrogen-bond energy (E_H,tot) leads to a higher melting point. The order of cations and anions on charge transfer (q), second-order perturbation energy (E₂), and binding energy (E_b) are the same to that of E_H,tot, so larger q leads to larger E₂, E_b, and E_H,tot. All salts have similar frontier orbitals distributions, and their HOMO and LUMO are derived from the anion and the cation, respectively. The molecular orbital shapes are kept as the ions form a salt. To produce energetic salts, 5-aminotetrazole and HClO₄ are the preferred base and acid, respectively.

The structures of hydrazinium dinitramide (HDN) in the gas phase and in aqueous solution have been studied at different levels of theory by using quantum chemistry. The intramolecular hydrogen-bond interactions in HDN were studied by employing the quantum theory of atoms in molecules (QTAIM), as well as those in ammonium dinitramide (ADN), hydrazinium nitroformate (HNF), and ammonium nitroformate (ANF) for comparison. The results showed that HDN possessed the strongest hydrogen bonds, with the largest hydrogen-bond energy (−47.95 kJ mol⁻¹) and the largest total hydrogen-bond energy (−60.29 kJ mol⁻¹). In addition, the charge transfer between the cation and the anion, the binding energy, the energy difference between the frontier orbitals, and the second-order perturbation energy of HDN were all the largest among the investigated compounds. These strongest intramolecular interactions accounted for the highest decomposition temperature of HDN among all four compounds. The IR spectra in the gas phase and in aqueous solution were very different and showed the significant influence of the solvent. The UV spectrum showed the strongest absorption at about 253 nm. An orbital-interaction diagram demonstrated that the transition of electrons mainly happened inside the anion of HDN. The detonation velocity (D=8.34 km s⁻¹) and detonation pressure (P=30.18 GPa) of HDN were both higher than those of ADN (D=7.55 km s⁻¹ and P=24.83 GPa). The composite explosive HDN/CL-20 with the weight ratio w_CL−20/w_HDN=0.388:0.612 showed the best performance (D=9.36 km s⁻¹, P=39.82 GPa), which was close to that of CL-20 (D=9.73 km s⁻¹, P=45.19 GPa) and slightly better than that of the composite explosive ADN/CL-20 (w_CL−20/w_ADN=0.298:0.702, D=9.34 km s⁻¹, P=39.63 GPa).

In this work, a set of derivatives of 2-(5-amino-3-nitro-1,2,4-triazolyl)-3,5-dinitropyridine (PRAN) with different energetic substituents (−N₃, –NO₂, –NH₂, –NF₂) have been studied at the Becke, three-parameter, Lee–Yang–Parr/aug-cc-pvdz, Becke, three-parameter, Lee–Yang–Parr/6-31G(d), Becke, three-parameter, Perdew 86/6-31G(d), and Becke three-parameter, Perdew–Wang 91/6-31G(d,p) levels of density functional theory. The gas-phase heats of formation were predicted with isodesmic reactions and the condensed-phase HOFs were estimated with the Politzer approach. The effects of different functionals and basis sets were analyzed. –N₃ and –NO₂ greatly increase while –NH₂ and –NF₂ slightly decrease heats of formation. An analysis of the bond dissociation energies and impact sensitivity shows that all compounds have good stability. The crystal densities (1.82–2.00 g/cm³) computed from molecular packing calculations are big for all compounds and that of the –NF₂ derivative is the largest. All derivatives have higher detonation velocity and detonation pressure than PRAN. Compounds 3 and 4 (R = NO₂ and NF₂) have better performance than hexahydro-1,3,5-trinitro-1,3,5-trizine and the performance of 4 is quite close to that of 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane, they are promising candidates of high energy compounds and worth further investigations. Copyright © 2012 John Wiley & Sons, Ltd.

Under different temperatures and concentrations, the diffusion of Vitamin C (VC) in water solution was examined by molecular dynamics simulation. The diffusion coefficients were calculated based on the Einstein equation. The influences of temperature, concentration, and simulation time on the diffusion coefficient were discussed. The results showed that at higher temperature and lower concentration the normal diffusions appear relatively late, but the linear range of mean square displacement curves continues longer than that at lower temperature and higher concentration. At the same temperature, the normal diffusion time increases and the diffusion coefficient decreases as the simulation concentration increases. These simulation results are in good agreement with experiments. Analyses of the pair correlation functions of the simulation systems showed that hydrogen bonds are mainly formed between the hydrogen atoms of VC molecules and oxygen atoms of H₂O molecules, rather than between the O atoms of VC molecules and H atoms of H₂O molecules. The diffusion coefficient is higher as the interaction between water molecules and VC molecules is stronger when VC concentration is lower. The water in the model systems affects the diffusion of VC molecules by the short-range repulsion of O(H₂O)-O(H₂O) pairs and the non-bond interaction of H(H₂O)-H(H₂O) pairs. The short-range repulsion of O(H₂O)-O(H₂O) pairs is greater when VC concentration is higher, the diffusion of VC is weaker. The greater the non-bond interaction of H(H₂O)-H(H₂O) pairs is, the higher the VC diffusion is. It is expected that this study can provide a theoretical direction for the experiments on the mass transfer of VC in water solution.

The intramolecular hydrogen-bonding interactions and properties of a series of nitroamino[1,3,5]triazine-based guanidinium salts were studied by using the dispersion-corrected density functional theory method (DFT-D). Results show that there are evident LP(N or O; LP=lone pair)σ*(NH) orbital interactions related to O⋅⋅⋅HN or N⋅⋅⋅HN hydrogen bonds. Quantum theory of atoms in molecules (QTAIM) was applied to characterize the intramolecular hydrogen bonds. For the guanidinium salts studied, the intramolecular hydrogen bonds are associated with a seven- or eight-membered pseudo-ring. The guanylurea cation is more helpful for improving the thermal stabilities of the ionic salts than other guanidinium cations. The contributions of different substituents on the triazine ring to the thermal stability increase in the order of NO₂<NF₂<N₃ (ONO₂)<NH₂. Energy decomposition analysis shows that the salts are stable owing to electrostatic and orbital interactions between the ions, whereas the dispersion energy has very small contributions. Moreover, the salts exhibit relatively high densities in the range of 1.62–1.89 g cm⁻³. The detonation velocities and pressures lie in the range of 6.49–8.85 km s⁻¹ and 17.79–35.59 GPa, respectively, which makes most of them promising explosives.

Ninety-one nitro and hydroxyl derivatives of benzene were studied at the B3LYP/6-31G∗ level of density functional theory. Detonation properties were calculated using the Kamlet-Jacobs equation. Three candidates (pentanitrophenol, pentanitrobenzene, and hexanitrobenzene) were recommended as potential high energy density compounds for their perfect detonation performances and reasonable stability. The pyrolysis mechanism was studied by analyzing the bond dissociation energy (BDE) and the activation energy (E_a) of hydrogen transfer (H–T) reaction for those with adjacent nitro and hydroxyl groups. The results show that E_a is much lower than BDEs of all bonds, so when there are adjacent nitro and hydroxyl groups in a molecule, the stability of the compound will decrease and the pyrolysis will be initiated by the H–T process. Otherwise, the pyrolysis will start from the breaking of the weakest C–NO₂ bond, and only under such condition, the Mulliken population or BDE of the C–NO₂ bond can be used to assess the relative stability of the compound.

HNAB (2,2′,4,4′,6,6′-hexanitroazobenzene) and its derivatives have been optimized to obtain their molecular geometries and electronic structures by using density functional theory at the B3LYP/6-31G* level. Their IR spectra have been computed and assigned by vibrational analysis. The strongest peaks are attributed to the NO asymmetric stretching of nitro groups. Its central position moves towards higher frequency as the number of nitro groups increases. It is obvious that there is hydrogen-bonding between amino and nitro groups in amino derivatives. Based on the frequencies scaled by 0.96 and the principle of statistical thermodynamics, the thermodynamic properties have been evaluated, which are linearly related with the temperature, as well as the number of nitro and amino groups, respectively, obviously showing good group additivity. And the thermodynamic functions for the nitro derivatives increase much more than those for the amino derivatives with the increase of the number of substituents. The values of heat of formation (HOF) for the nitro derivatives increase gradually with n, while those of the amino derivatives decrease smoothly with n.

The interactions between calcite crystal and seven kinds of phosphonic acids, nitrilotris(methylphosphonic acid) (NTMP), nitrilo-methyl-bis(methylphosphonic acid) (NMBMP), N,N-glycine-bis(methylphosphonic acid) (GBMP), 1- hydroxy-1,1-ethylenebis(phosphonic acid) (HEBP), 1-amino-1,1-ethylenebis(phosphonic acid) (AEBP), 1,2-ethylenediamine-N,N,N′,N′-tetrakis(methylphosphonic acid) (EDATMP), and 1,6-hexylenediamine-N,N,N′,N′-tetrakis- (methylphosphonic acid) (HDATMP) have been simulated by a molecular dynamics method. The results showed that the binding energy of each scale inhibitor with the (1l̄0) (1l̄0) face of calcite crystal was higher than that with (104) face, which has been approved by the analysis of pair correlation functions. The sequence of scale inhibition efficiencies for phosphonic acids against calcite scale is as follows: EDATMP>HDATMP>HEBP>NTMP>GBMP>HEBP>NMBMP, and the growth inhibition on the (1l̄0) face of calcite was at the leading status. Phosphonic acids deformed during the binding process, and electrovalent bonds formed between the phosphoryl oxygen atoms in phosphonic acids and the calcium ions on calcite crystal.