Potential High Energy Density Research Articles

Stability, detonation properties and pyrolysis mechanisms of polynitrotriprismanes C6H6−n(NO2)n (n=1−6)

To further test whether polynitriprismanes are capable of being potential high energy density materials (HEDMs), extensive theoretical calculations were carried out to investigate on a series of polynitrotriprismanes (PNNPs): C6H6−n(NO2)n (n=1−6). Heats of formation (HOFs), strain energies (SE), and disproportionation energy (DE) were obtained using B3LYP/6-311+G(2df, 2p)//B3LYP/6-31G* method by designing different isodesmic reactions, respectively. Detonation properties of PNNPs were obtained by the well-known KAMLET-JACOBS equations, using the predicted densities (ρ) obtained by Monte Carlo method and HOFs. It is found that they increase as the number of nitro groups n varies from 1 to 6, and PNNPs with n≥4 have excellent detonation properties. The relative stability and the pyrolysis mechanism of PNNPs were evaluated by the calculated bond dissociation energy (BDE). The comparison of BDE suggests that rupturing the C-C bond is the trigger for thermolysis of PNNPs. The computed BDE for cleavage of C-C bond (88.5 kJ/mol) further demonstrates that only the hexa-nitrotriprismane can be considered to be the target of HEDMs.

DFT Studies on a High Energy Density Cage Compound 4-Trinitroethyl-2,6,8,10,12-pentanitrohezaazaisowurtzitane

Polynitro cage compound 4-trinitroethyl-2,6,8,10,12-pentanitrohexaazaisowurtzitane has the same framework with but higher stability than CL-20 and is a potential new high energy density compound (HEDC). In this paper, the B3LYP/6-31G(d,p) method of density functional theory (DFT) has been used to study its heat of formation, IR spectrum, and thermodynamic properties. The stability of the compound was evaluated by the bond dissociation energies. The calculated results show that the first step of pyrolysis is the rupture of the N-NO(2) bond in the side chain and verify the experimental observation that the title compound has better stability than CL-20. The crystal structure obtained by molecular mechanics belongs to the P2(1)2(1)2(1) space group, with lattice parameters a = 12.59 Å, b = 10.52 Å, c = 12.89 Å, Z = 4, and ρ = 2.165 g·cm(-3). Both the detonation velocity of 9.767 km·s(-1) and the detonation pressure of 45.191 GPa estimated using the Kamlet-Jacobs equation are better than those of CL-20. Considering that this cage compound has a better detonation performance and stability than CL-20, it may be a superior HEDC.

DFT Studies on Detonation Properties, Pyrolysis Mechanism, and Stability of the Nitro and Hydroxyl Derivatives of Benzene

AbstractNinety‐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 (Ea) of hydrogen transfer (H–T) reaction for those with adjacent nitro and hydroxyl groups. The results show that Ea 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.

Theoretical studies on a series of 1,2,3-triazoles derivatives as potential high energy density compounds

Based on the full-optimized molecular geometric structures at B3LYP/6-31G* and B3P86/6-31G* levels, the densities (ρ), detonation velocities (D), and pressures (P) for a series of 1,2,3-triazole derivatives, as well as their thermal stabilities, were investigated to look for high energy density compounds (HEDCs). The heats of formation (HOFs) are also calculated via designed isodesmic reactions. The calculations on the bond dissociation energies (BDEs) indicate that the BDEs of the initial scission step are between 53 and 70 kcal/mol, and 4-nitro-1,2,3-triazole is the most reactive compound, while 1-(2′,4′-dinitrophenyl)-5-nitro-1,2,3-triazole is the least reactive compound for 1,2,3-triazole derivatives studied. The condensed phase heats of formation are also calculated for the title compounds. These results would provide basic information for the further studies of HEDCs. The detonation data of 1-(3′,4′-dinitrophenyl)-4-nitro-1,2,3-triazole and 1-(2′,4′-dinitrophenyl)-4-nitro-1,2,3-triazole show that they meet the requirement for HEDCs.

Potential high-energy pentazolides: HB(N5 )3 M1∼2 (N5 )3 BH (M = Be, Mg, Ca, Zn, and Cd)

HB(N5)3M1∼2(N5)3BH (M = Be, Mg, Ca, Zn, and Cd) have been investigated as potential high-energy density materials in this article by means of density functional theory. They are all of high-energy content and show kinetic stability as to the breakup of N5 ring, especially HB(N5)3Mg(N5)3BH. The MN bondings in the mononuclear compounds are stronger than those in the corresponding dinuclear ones, except in the Be analogues. Furthermore, except HB(N5)3Zn2(N5)3BH, all the dinuclear compounds are shown to be energetically stable with respect to disproportionation. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Theoretical studies on polynitro-1,3-bishomopentaprismanes as potential high energy density compounds

Based on the fully optimized molecular geometric structures at the DFT-B3LYP/6-31G* level, the densities ( ρ), detonation velocities ( D) and pressures ( P) for a series of polynitro-1,3-bishomopentaprismanes (PNBPPs), as well as their thermal stabilities, were investigated to look for high energy density compounds (HEDCs). The studied PNBPPs have high values of heats of formation (HOFs) and the magnitude is correlative with the number ( n) and the space distance of nitro groups. D and P for PNBPPs were estimated by using modified Kamlet–Jacobs equations based on the calculated HOFs and ρ. It is found that ρ, D and P all increase with n and satisfy the group additivity rule. The calculations on the bond dissociation energies of C NO 2 and C C bonds indicate that both bonds are possible to be the trigger bond in the pyrolysis process, and this interesting phenomenon is related with the molecular structure, especially the strain energy of the skeleton. In conjunction with the energetic performances and thermal stabilities, PNBPPs with n = 8–12 are recommended as the preferred candidates of HEDCs. These results would provide basic information for the further studies of PNBPPs.

HB(N 5) 3M (M = Li, Na, K, and Rb): A new kind of pentazolides as HEDMs

HB(N 5) 3M (M = Li, Na, K, and Rb) have been investigated as potential high-energy density materials in the present paper by means of density functional theory. They all show kinetic stabilities as to the breakup of N 5 ring. Their kinetic stabilities decrease in the order of Li, Na, K, and Rb. Compared to HB(N 5) 3K and HB(N 5) 3Rb, HB(N 5) 3Li and HB(N 5) 3Na have higher transition state barriers and are of significantly higher energy content, and thus they are suggested to be more practical and suitable as potential high-energy density materials.

Theoretical studies on new potential high energy density compounds (HEDCs) adamantyl nitrates from gas to solid

A series of adamantyl nitrates have been theoretically studied from gas to solid to search for new potential high energy density compounds (HEDCs). The heats of formation (HOFs) for the 26 title compounds were calculated by designing isodesmic reactions at the B3LYP/6-31G* level. It was found that the HOFs of the 26 isomers with the same number of -ONO2 groups (n) are not correlated well with the corresponding substituted positions. According to the obtained heats of detonation (Q), detonation velocities (D), and detonation pressures (P) using the Kamlet-Jacobs equations, it was found that when n=7∼8, the adamantyl nitrates meet the criterion as an HEDC. The calculations on bond dissociation energies of O-N (EO-N) showed that the adamantyl nitrates with gemi- ONO2 always have the worst stability among the isomers, and all the adamantyl nitrates with gemi- ONO2 have similar stability. Due to the complexity of their structures, values of EO-N do not decrease with the increase of the substituent number n obviously, and the stability of adamantyl nitrates is not determined by only one structural parameter. Considering the stability requirement, only 1,2,4,6,8,9,10-adamantyl heptanitrate is recommended as a feasible HEDC. Molecular packing searching for 1,2,4,6,8,9,10-adamantyl heptanitrate among 7 most possible space groups (P21/c, P-1, P212121, P21, Pbca, C2/c, and Pna21) using Compass and Dreiding force fields showed that this compound tends to crystallize in P21/c. Ab initio periodic calculations on the electronic structure of the predicted packing showed that the O-NO2 bond is the trigger bond during thermolysis, which agrees with the result derived from the study of dissociation energies of O-N bonds.

Molecular Packing Prediction and Periodic Calculations on Three Polynitroadamantanes as Potential High Energy Density Compounds

AbstractThe DREIDING force field was chosen to predict the molecular packings for the three polynitroadamantanes (PNAs) with 8–10 ‐NO2 among the 7 most possible space groups (P21/c, P‐1, P212121, P21, Pbca, C2/c and Pna21) using molecular mechanics (MM) method, respectively. Then, ab inito periodic calculations were performed on the three predicted crystals using the DFT‐GGA‐RPBE method. Density of states (DOS) calculations showed that C–N bond was the trigger bond of PNA during thermolysis; band gaps (ΔE) were used to predict their relative sensitivity. All of these are consistent well with those drawn from bond dissociation energy calculation on gas molecules. Besides, our calculations present that variations of PNAs molecular structures from gas to crystal become smaller with the number of ‐NO2 groups increasing.

Potential high-energy compounds: H2N5M1∼2N5H2 (M = Be, Mg, Ca, Zn, and Cd)

As potential high-energy density materials, H2N5M1∼2N5H2 (M = Be, Mg, Ca, Zn, and Cd) have been investigated by means of density functional theory. They all show high stability with respect to the dissociation into and . The mononuclear compounds H2N5MN5H2 are more stable than the corresponding dinuclear ones, except the Be analogies. The H2N5 fragment is indeed stabilized by an electron attachment. The H2N5M1∼2N5H2 (M = Be, Mg, Ca, Zn, and Cd) species might be observed experimentally, especially H2N5Be1∼2N5H2, H2N5MgN5H2, and H2N5ZnN5H2.

Theoretical predictions on the structures and properties for polynitrohexaazaadamantanes (PNHAAs) as potential high energy density compounds (HEDCs)

It is the heated point to make molecular design of high energy density compounds (HEDCs) in the world energy and resource field. However, previous works usually were ended with gas molecular design. On the other hand, most of high energy materials are in agglomerate phase, especially in crystals. In this paper, we make crystal structure predictions for the potential HEDCs, polynitrohexaazaadamantanes (PNHAAs), by choosing appropriate force field using molecular mechanics (MM) method. Based on the ab initio periodic calculations on their predicted packings, their electronic structures (density of states, DOS) and properties, such as sensitivity and thermolysis mechanism were investigated. Besides, we make comparisons between the conclusions drawn from gas and solid calculations. It is most interesting that our calculations predict that 2,4,6,8,9,10-hexanitrohexaazaadamantane may possess better properties than the well-known HEDC ε-CL-20 (hexanitrohexaazaisowurtzitane).

Electronic Structure Studies of Tetrazolium-Based Ionic Liquids

New energetic ionic liquids are investigated as potential high energy density materials. Ionic liquids are composed of large, charge-diffuse cations, coupled with various (usually oxygen containing) anions. In this work, calculations have been performed on the tetrazolium cation with a variety of substituents. Density functional theory (DFT) with the B3LYP functional, using the 6-311G(d,p) basis set was used to optimize geometries. Improved treatment of dynamic electron correlation was obtained using second-order perturbation theory (MP2). Heats of formation of the cation with different substituent groups were calculated using isodesmic reactions and Gaussian-2 calculations on the reactants. The cation was paired with oxygen rich anions ClO4-, NO3-, or N(NO2)2- and those structures were optimized using both DFT and MP2. The reaction pathway for proton transfer from the cation to the anion was investigated.

Structures and enthalpies of methyl- and dimethyl-1,3-dioxa-2,4-diazetidine, CH 3HN 2O 2 and (CH 3) 2N 2O 2. High-level calculations

As a follow-up to a study of dioxadiazetidine, N 2H 2O 2, as a potential high energy density material, we determined optimized geometries, vibrational frequencies, and enthalpies of formation and combustion of its organic derivatives 2-methyl-1,3-dioxa-2,4-diazetidine and 2,4-dimethyl-1,3-dioxa-2,4-diazetidine, both of which would exist as cis and trans isomers. As a fundamental measure of the reactivity of the two compounds, the proton affinities of both isomers were also determined. Gaussian-2, Gaussian-3, and two complete basis set methods were used.

Computational Studies on Polynitrohexaazaadmantanes as Potential High Energy Density Materials

Polynitrohexaazaadamantanes (PNHAAs) have been the subject of much recent research because of their potential as high energy density materials (HEDMs). The B3LYP/6-31G method was employed to evaluate the heats of formation (HOFs) for PNHAAs by designing isodesmic reactions. The HOFs are found to be correlative with the number (n) and the space orientations of nitro groups. Detonation velocities (D) and detonation pressures (P) were estimated for PNHAAs by using the well-known Kamlet-Jacobs equations, based on the theoretical densities (rho) and HOFs. It is found that D and P increase as n ranges from 1 to 6, and PNHAAs with 4-6 nitro groups meet the criteria of an HEDM. When n is over 6, rho of PNHAAs slightly increases; however, the chemical energy of detonation (Q) decreases so greatly that both D and P decrease. The calculations on bond dissociation energies suggest that the N-N bond be the trigger bond during the pyrolysis initiation process of each PNHAA, and with increasing n, N-N bond dissociation energy (E(N-N)) decreases on the whole, that is to say, the relative stability of PNHAAs decreases. All E(N-N)(s) of PNHAAs are more than 30 kcal.mol(-1), which further proves that four PNHAAs with 4-6 nitro groups can be used as the candidates of HEDMs. Considering the synthesis difficulty and the performance as an energetic compound, we finally recommended 2,4,6,8,10-pentanitrohexaazaadamantane as the target HEDM for PNHAAs.

New potential high-energy materials: Oxadiaziridine, N 2H 2O. High-level calculations

A recent suggestion that oxadiaziridine, N 2H 2O, might act as a potential high-energy density material prompts us to determine the enthalpies of formation and combustion of the two conformational isomers of this compound. As a fundamental measure of the reactivity of N 2H 2O, the proton affinity of both isomers was also determined. Gaussian-2, Gaussian-3, and two complete basis set methods were used.

Ab Initio Calculations on the (1)2Δ Excited State and Low-Lying Quartet States of Ga·N2: Simulation of Its LIF Spectrum

The (2)Delta and (4)Sigma (-) excited states of Ga .N-2, which were assigned by Ellis et al. (Phys. Chem. Chem. Phys. 1999, 1, 2709) to the upper states of two LIF transitions observed from the Ga .N-2 (X) over tilde (2)Pi State with onsets of 33468 and 37633 cm(-1), respectively, have been studied by high-level ab initio calculations. Minimum-energy geometrical parameters, harmonic vibrational frequencies, and relative energies were computed at the SERHF, CASSCF, B3LYP, MP2, QCISD, and CCSD(T) levels of calculation, using standard and specifically designed, all-electron and ECP (for Ga) basis sets of up to aug-cc-pVQZ quality. In addition, the low-lying linear (4)Pi and a number of T-shaped quartet states of Ga .N-2 were also studied. Franck-Condon factors (FCFs) of selected electronic transitions were calculated. Absorption spectra were simulated by employing the computed FCFs. On the basis of ab initio results and spectral simulations, the assignment of the 33468 cm(-1) LIF band is concluded to be the (2)Delta (3/2) 200 cm(-1)). In addition, all low-lying Ga .N-2 quartet states considered were found to be either very weakly bound van der Waals states (Ga-N bond length ca. 5 Angstrom) or well-bound charge transfer states, and none of them can be assigned to the upper state of this LIF band. Doubts concerning the identity of the molecular carrier and the electronic states involved in this LIF band remain. Finally, the stabilities of the charge-transfer quartet states of Ga .N-2 investigated in this work have been rationalized in terms of bonding interaction between the HOMOs of Ga and the LUMOs of N-2 and electrostatic attraction resulting from charge transfer from Ga to N-2. Possible applications of this kind of bonding and charge-transfer interactions in an M .N-4 ring system have been discussed briefly in relation to stabilizing an N-n system, where M .N-n represents a potential high energy density material.

Theoretical study of the N10 clusters without double bonds

Quantum chemical ab initio methods have been used to examine nine N10 clusters without double bonds. In additional to the three N10 isomers previously studied in the literature, six new N10 structures were investigated. Fully geometry optimization, harmonic vibrational frequency, and thermodynamics calculation of nine different N10 molecules were performed at the RHF/6-31G*, B3LYP/6-31G*, and MP2/6-31G* levels. All of the nine structures were found to be local minima on the energy hypersurface at the RHF/6-31G* level, whereas eight structures are stable at the B3LYP/6-31G* level. At the MP2/6-31G* level, seven local minima were found. They would be potential high-energy density material (HEDM). According to the results presented herein, the structure N10[V(C2v)] is the most stable molecule of all the N10 clusters without double bonds. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 34–43, 2001

Metal atoms trapped in cryogenic matrices as potential rocket fuels

Metal atom dispersions in cryogenic matrices are potential high-energy density rocket fuels. Using the 7sp extractable to rate a fuel, we have examined the potential of a family of in fuels, in combination with liquid oxygen or liquid fluorine oxidizers. The fuels studied were composed of a dispersion of light metal atoms in a molecular hydrogen matrix. The 7sp was calculated using a thermodynamic code designed for rocket combustion. The code requires accurate values for the enthalpy of formation of the fuel (A///(fuel)). For any particular total metal mole fraction (i.e., loading) the metal in matrix fuel will contain a distribution of metalbearing species. Each will have its own characteristic A//y. The weighted sum of these yields A/f/(fuel). Consequently, accurate calculation of A///(fuel) requires that this population, the relative concentrations of free metal atoms, dimers, and metal bearing clusters, be accurately described. A statistical model was devised to predict this distribution. Using it, the enthalpy of formation of the fuel was computed. We find that several members of the family studied have, in combination with either liquid oxygen or fluorine, an 7sp potential significantly greater than that which characterizes the best currently available fuel/oxidized combination. In general, for all the family members studied, the maximum 7sp is extracted when the metal atom concentration is maximized, and under these circumstances the oxidizer reacts exclusively with the metal inclusions while the matrix behaves as the system's working fluid. Finally these predictions, based on our statistical model of the distribution of metal bearing species, were compared with predictions based on models in which 1) only metal atoms and dimers are present in the matrix, or 2) only selectively positioned metal atoms are included in the matrix.

Is there a transition state for the unimolecular dissociation of cyclotetraoxygen (O4)?

The cyclo-O4 molecule is isoelectronic with cyclobutane and has been mentioned as a potential new high energy density material (HEDM). The important unresolved question has been whether or not cyclo-O4 is a genuine minimum on the O4 potential energy hypersurface. Here the transition state for cyclo-O4 dissociation to two O2 molecules has been located at a number of levels of theory using a double zeta plus polarization (DZP) basis set. The theoretical methods with which the transition state geometry was optimized include two-configuration self-consistent-field (TCSCF), configuration interaction including all single and double excitations (CISD), coupled cluster including all single and double excitations (CCSD), and the latter with a noniterative correction for connected triple excitations, CCSD(T). The equilibrium geometry of O4 has D2d symmetry, while a stationary point of D2 symmetry is of Hessian index two (i.e., two imaginary vibrational frequencies) at the highest level of theory, DZP CCSD(T). The true transition state lies only slightly lower energetically (classical barrier 7.9 kcal/mole) and is of C2 symmetry with the DZP CCSD(T) method. The activation energy was predicted in a completely consistent manner to be 6.2 kcal/mole. The possibility that this barrier could disappear entirely at higher levels of theory is discussed. It is concluded that the O4 barrier is too low for O4 to be useful as a HEDM.

Potential new high energy density materials: Cyclooctaoxygen O8, including comparisons with the well-known cyclo-S8 molecule

The cyclic O8 molecule has been studied using ab initio quantum mechanical methods. Molecular structures were fully optimized at levels of theory up to and including second-order perturbation theory (MP2) using a double zeta plus polarization basis set. Parallel theoretical studies were carried out for the valance isoelectronic S8 molecule, for which much experimental data exists. With double zeta plus polarization (DZ+P) self-consistent-field (SCF) theory vibrational frequencies and infrared and Raman intensities have been predicted. Cyclo-O8 is considerably more stable than experimental O–O bond energies would suggest and is predicted to lie only 94 kcal/mol above four infinitely separated O2 molecules.