Heming Xiao

Molecular Design of 1,2,4,5-Tetrazine-Based High-Energy Density Materials

The heats of formation (HOFs) for a series of 1,2,4,5-tetrazine derivatives were calculated by using density functional theory (DFT), Hartree Fork (HF), and Møller-Plesset (MP2) as well as semiempirical methods. The effects of different basis bets on HOFs were also considered. Our results show that the -CN or -N3 group plays a very important role in increasing the HOF values of the 1,2,4,5-tetrazine derivatives. An analysis of the bond dissociation energies for the weakest bonds indicates that substitutions of the -N3, -NH2, -CN, -OH, or -Cl group are favorable for enhancing the thermal stability of 1,2,4,5-tetrazine, but the -NHNH2, -NHNO2, -NO2, -NF2, or -COOH group produces opposite effects. The calculated detonation velocities and pressures indicate that the -NF2 or -NO2 group is very helpful for enhancing the detonation performance for the derivatives, but the case is quite the contrary for the -CN, -NH2, or -OH group. Considered the detonation performance and thermal stability, three derivatives may be regarded as potential candidates of high-energy density materials (HEDMs).

Computational studies on the infrared vibrational spectra, thermodynamic properties, detonation properties, and pyrolysis mechanism of octanitrocubane

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 726.47 kJ/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 220.63 kJ/mol, 2.189 g/cm3, and 505.84 kJ/mol, respectively. In addition, the estimated detonation velocity and detonation pressure of ONC are 10.26 mm/ms and 520.86 kbar, 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 resul...

DFT study on energetic tetrazolo-[1,5-b]-1,2,4,5-tetrazine and 1,2,4-triazolo-[4,3-b]-1,2,4,5-tetrazine derivatives

The heats of formation (HOFs) for a series of tetrazolo-[1,5-b]-1,2,4,5-tetrazine (TETZ) and 1,2,4-triazolo-[4,3-b]-1,2,4,5-tetrazine (TTZ) derivatives were studied by using density functional theory. The results show that the substitution of the -N(3) or -N(NO(2))(2) group in the TETZ or TTZ ring extremely enhances its HOF values. For monosubstituted case, attachment of a substituent to position 8 in the TETZ or TTZ ring will increase its energy gaps except for the derivatives with the -NO(2) group. It is also found that the energy gap of TTZ can be tuned by incorporating a substituent into different positions in the parent ring. The substitution of the -NH(2) group in the TETZ ring is favorable for enhancing its thermal stability. For the TTZ ring, different substituted positions and number of the substituent might affect its thermal stability. The calculated detonation properties indicate that incorporating the -NO(2), -NF(2), -ONO(2), or -N(NO(2))(2) group into the TETZ or TTZ ring is very helpful for enhancing its detonation performance. Considered the detonation performance and thermal stability, four derivatives may be regarded as the promising candidates of high-energy density materials (HEDMs).

Comparative theoretical studies of energetic substituted carbon- and nitrogen-bridged difurazans.

Density functional theory method was used to study the heats of formation (HOFs), electronic structure, energetic properties, and thermal stability for a series of bridged difurazan derivatives with different linkages and substituent groups. The results show that the -N(3) group and azo bridge (-N=N-) play a very important role in increasing the HOF values of the difurazan derivatives. The effects of the substituents on the HOMO-LUMO gap are combined with those of the bridge groups. The calculated energetic properties indicate that the -ONO(2), -NO(2), -NF(2), -N=N-, or -N(O) =N- group is an effective structural unit for enhancing the detonation performance for the derivatives. An analysis of the bond dissociation energies for several relatively weak bonds suggests that the N-O bond in the ring is the weakest one and the ring cleavage is possible to happen in thermal decomposition. On the whole, the -NH-NH-, -N=N-, or -N(O)=N- group is an effective bridge for enhancing the thermal stability of the derivatives. Considered the detonation performance and thermal stability, five compounds may be considered as the potential candidates of high-energy density materials (HEDMs).

Impact sensitivity and activation energy of pyrolysis for tetrazole compounds

Calculations with both DFT-B3LYP and semiempirical quantum chemical PM3 methods are carried out on a series of tetrazole derivatives and their metal salts to investigate the relationship between the relative order of impact sensitivity and activation energy of thermal decomposition. The results show that the relative order of sensitivity for the titled compounds can be predicted by examining the activation energy for breaking down of tetrazole ring.

A new design strategy for high-energy low-sensitivity explosives: combining oxygen balance equal to zero, a combination of nitro and amino groups, and N-oxide in one molecule of 1-amino-5-nitrotetrazole-3N-oxide

We report a new strategy to design a novel high-energy low-sensitivity explosive, 1-amino-5-nitrotetrazole-3N-oxide (ANTZO), with outstanding overall performance by combining oxygen balance equal to zero, a combination of nitro and amino groups, and N-oxide in one molecule. Its detonation performance and stability were estimated using the density functional theory method and compared with some well-known explosives such as 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and 1-methyl-2,4,6-trinitrobenzene (TNT). Its heat of detonation (7.03 kJ g−1) and detonation velocity (9.87 km s−1) are larger than those of CL-20, while its h50 value (29 J) is higher than that of TNT, indicating that ANTZO has both the high detonation performance of CL-20 and the low sensitivity of TNT, making it valuable and attractive for experiments. Intramolecular hydrogen transfer is the initial decomposition step of ANTZO with the activation energy for this thermal decomposition reaction being about 51.5 kcal mol−1. Our results indicate that our new strategy used for designing ANTZO is practical and may be applied to design and develop other explosives with high energetic properties and low sensitivity.

Molecular dynamics simulations of RDX and RDX-based plastic-bonded explosives

Molecular dynamics simulations have been performed to investigate well-known energetic material cyclotrimethylene trinitramine (RDX) crystal and RDX-based plastic-bonded explosives (PBXs) with four typical fluorine-polymers, polyvinylidenedifluoride (PVDF), polychlorotri-fluoroethylene (PCTFE), fluorine rubber (F(2311)), and fluorine resin (F(2314)). The elastic coefficients, mechanical properties, binding energies, and detonation performances are obtained for the RDX crystal and RDX-based PBXs. The results indicate that the mechanical properties of RDX can be effectively improved by blending with a small amount of fluorine polymers and the overall effect of fluorine polymers on the mechanical properties of the PBXs along three crystalline surfaces is (001)>(010) approximately (100) and PVDF is regarded to best improve the mechanical properties of the PBXs on three surfaces. The order of the improvement in the ductibility made by the fluorine polymers on different surfaces is (001) approximately (010)>(100). The average binding energies between different RDX crystalline surfaces and different polymer binders are obtained, and the sequence of the binding energies of the PBXs with the four fluorine polymers on the three different surfaces is varied. Among the polymer binders, PVDF is considered as best one for RDX-based PBXs. The detonation performances of the PBXs decrease in comparison with the pure crystal but are superior to those of TNT.

Molecular dynamics study of binding energies, mechanical properties, and detonation performances of bicyclo-HMX-based PBXs.

To investigate the effect of polymer binders on the monoexplosive, molecular dynamics simulations were performed to study the binding energies, mechanical properties, and detonation performances of the bicyclo-HMX-based polymer-bonded explosives (PBXs). The results show that the binding energies on different crystalline surfaces of bicyclo-HMX decrease in the order of (010)>(100)>(001). On each crystalline surface, binding properties of different polymers with the same chain segment are different from each other, while those of the polymers in the same content decrease in the sequence of PVDF>F(2311)>F(2314) approximately PCTFE. The mechanical properties of a dozen of model systems (elastic coefficients, various moduli, Cauchy pressure, and Poissons ratio) have been obtained. It is found that mechanical properties are effectively improved by adding small amounts of fluorine polymers, and the overall effect of fluorine polymers on three crystalline surfaces of bicyclo-HMX changes in the order of (010)>(001) approximately (100). In comparison with the base explosive, detonation performances of the PBXs decrease slightly, but they are still superior to TNT. These suggestions may be useful for the formulation design of bicyclo-HMX-based PBXs.

Density functional theory study of piperidine and diazocine compounds.

Density functional theory calculations at the B3LYP/6-311G** level were performed to predict the heats of formation (HOFs) for three eight-membered ring compounds and four six-membered ring compounds via designed isodesmic reactions. In the isodesmic reactions designed for the computation of HOFs (CH(3)CH(2))(2)NNO(2) and piperidine were chosen as reference compounds. The HOFs for -NO(2) substituted derivations are larger than those of -NF(2) substituent groups. Thermal stability were evaluated via bond dissociation energies (BDE) at the UB3LYP/6-311G** level. As a whole, the homolysis of CNF(2) or CNO(2) bonds is the main step for bond dissociation of the title compounds. Detonation properties of seven title compounds were evaluated by using the Kamlet-Jacobs equation based on the calculated densities and HOFs. It is found that 3,3,7,7-tetrakis(difluoroamino)octahydro-1,5-dinitro-1,5-diazocine (HNFX) and 3,3,5,5-tetrakis (difluoroamino)-1-nitro piperidine (N-nitro TDFAPP), with predicted density of ca. 2.0 g/cm(3), detonation velocity (D) about 9.9 km/s, and detonation pressure (P) of 47GPa that are lager than those of HMX, are expected to be the novel candidates of high energy density materials (HEDMs). The detonation data of 1,3,3,5,7,7-hexanitro-1,5-diazacyclooctane (HNDZ) and TNBDFAPP show that they meet the requirements for HEDMs.

A density functional theory investigation of 1,1-diamino-2,2-dinitroethylene dimers and crystal

The density functional method with different basis sets was applied to the study of the highly efficient and low sensitive explosive 1,1-diamino-2,2-dinitroethylene in both gaseous dimer and its bulk state. The binding energies have been corrected for the basis set superposition errors. Four stable dimers (I, II, III, and IV) were located. The corrected binding energy of the most stable dimer IV is predicted to be −38.15 kJ/mol at the B3LYP/6-311++G** level. It was found that the structure of the most stable dimer is just the basic packing pattern in the wave-shaped layer of 1,1-diamino-2,2-dinitroethylene solid phase. Vibrational modes associated with the N–C–N rocking exhibits blueshifts with large intensities as the results of large dipole moment changes, whereas those assigned to the stretching of N–H, which is bound by another submolecule, exhibit large redshifts (over −21 cm−1) with respect to those of the monomer. The changes of Gibbs free energies (ΔG) in the processes from the monomer to the dime...