Theoretical investigation on regulating photophysical properties and proton transfer behavior by electronegativity for near-infrared emitting styryl dyes.

Our main focus is to explore the atomic electronegativity-dependent photoinduced behavior of styryl derivatives (HBO, HBS, and HBSe). The results of structural parameter calculation by the DFT method show that the intramolecular hydrogen bonds of normal and tautomer form are strengthened and weakened, respectively, in an excited state (S1), which is conducive to the excited intramolecular proton transfer (ESIPT) process. The enhancement of excited hydrogen bond is beneficial to the ESIPT process from the aspects of infrared vibration frequency (IR), Mulliken's charge analysis, and density gradient reduction (RDG). Additionally, by determining the bond energy with the band critical point (BCP) parameter, we found that the lower the electronegativity of the atom, the larger the hydrogen bond strength at the excited state and the more likely ESIPT reaction occurs. Meanwhile, the intramolecular H-bonds O-H…N in HBO, HBS, and HBSe are enhanced with the weakened electron-withdrawing capacity of the atom (from O to S and Se). Subsequently, frontier molecular orbital (FMOs) and charge density difference (CDD) analyses essentially revealed that electron redistribution induces the ESIPT process. Low atomic electronegativity exhibits the high chemical activity of the excited state. Furthermore, to demonstrate the electronegativity-dependent ESIPT behavior of the system, we built potential energy curves (PECs) and located the transition states (TS) of proton transfer processes.

Decomposition mechanism of 1,3,5-trinitro-2,4,6-trinitroaminobenzene under thermal and shock stimuli using ReaxFF molecular dynamics simulations.

To obtain atomic-level insights into the decomposition behavior of 1,3,5-trinitro-2,4,6-trinitroaminobenzene (TNTNB) under different stimulations, this study applied reactive molecular dynamics simulations to illustrate the effects of thermal and shock stimuli on the TNTNB crystal. The results show that the initial decomposition of the TNTNB crystal under both thermal and shock stimuli starts with the breakage of the N-NO2 bond. However, the C6 ring in TNTNB undergoes structural rearrangement to form a C3-C5 bicyclic structure at a constant high temperature. Then, the C3 and C5 rings break in turn. The main final products of TNTNB under shock are N2, CO2, and H2O, while NO,  N2, H2O and CO are formed instead at 1 atm under a constant high temperature. Pressure is the main reason for this difference. High pressure promotes the complete oxidation of the reactants.

Coarse-grained force-field for large scale molecular dynamics simulations of polyacrylamide and polyacrylamide-gels based on quantum mechanics.

We developed a new coarse-grained (CG) molecular dynamics force field for polyacrylamide (PAM) polymer based on fitting to the quantum mechanics (QM) equation of state (EOS). In this method, all nonbond interactions between representative beads are parameterized using a series of QM-EOS, which significantly improves the accuracy in comparison to common CG methods derived from atomistic molecular dynamics. This CG force-field has both higher accuracy and improved computational efficiency with respect to the OPLS atomistic force field. The nonbond components of the EOS were obtained from cold-compression curves on PAM crystals with rigid chains, while the covalent terms that contribute to the EOS were obtained using relaxed chains. For describing PAM gels we developed water-PAM interaction parameters using the same method. We demonstrate that the new CG-PAM force field reproduces the EOS of PAM crystals, isolated PAM chains, and water-PAM systems, while successfully predicting such experimental quantities as density, specific heat capacity, thermal conductivity and melting point.

Encapsulating aluminum nanoparticles into carbon nanotubes for combustion: a molecular dynamics study.

Metal nanoparticles are easily deactivated by migration-aggregation in combustion. Encapsulated nanoparticles are one of the tools for coping with the stability challenges of metal nanoparticles. The self-assembly details of aluminum nanoparticles (ANPs) encapsulated into carbon nanotubes (CNTs) were demonstrated by molecular dynamics simulations. The simulation results show that ANPs can completely self-roll into CNTs to form a stable core-shell structure by inertial force and van der Waals force. Inside the tubes, ANPs move toward the cap at a velocity of 2.27 Å ps-1. However, it increases to 3.17 Å ps-1 when near the cap of CNTs. The initiation of the ANPs' oxidation and degradation can be effectively checked by coating CNTs. The diffusion of the Al atoms in the encapsulated ANPs occurred earlier than their oxidation in combustion, verified by using ReaxFF molecular dynamics simulations. The morphological evolutions of the nanostructures in the initial combustion of the encapsulated ANPs are predicted. The interplay between the encapsulated ANPs' responses and external stimuli is classified into core-shell separation, shell damage, and core-shell burst, which provides insights into the oxidation mechanism of encapsulated nanoparticles.

Theoretical Investigation of Energetic Salts with Pentazolate Anion.

Energetic salts based on pentazolate anion (cyclo-N5-) have attracted much attention due to their high nitrogen contents. However, it is an enormous challenge to efficiently screen out an appropriate cation that can match well with cyclo-N5-. The vertical electron affinity (VEA) of the cations and vertical ionization potential (VIP) of the anions for 135 energetic salts and some cyclo-N5- salts were calculated by the density functional theory (DFT). The magnitudes of VEA and VIP, and their matchability were analyzed. The results based on the calculations at the B3LYP/6-311++G(d,p) and B3LYP/aug-cc-pVTZ levels indicate that there is an excellent compatibility between cyclo-N5- and cation when the difference between the VEA of cation and the VIP of cyclo-N5- anion is -2.8 to -1.0 eV. The densities of the salts were predicted by the DFT method. Relationship between the calculated density and the experimental density was established as ρExpt = 1.111ρcal - 0.06067 with a correlation coefficient of 0.905. This regression equation could be in turn used to calibrate the calculated density of the cyclo-N5- energetic salts accurately. This work provides a favorable way to explore the energetic salts with excellent performance based on cyclo-N5-.

Effect of Nitrogen Cation as "Electron Trap" at π-Linker on Properties for p-Type Photosensitizers: DFT Study.

On the basis of thieno(3,2-b)thiophene and dithieno[3,2-b:2',3'-d]thiophene (T2 and T3 moieties) as π-linker, the A, D and S series dyes were designed to investigate the effect of the introducing N+ as an "electron trap" into T2 and T3 on the properties of the dyes. The optimized structures, electronic and optical properties were investigated by the density functional theory (DFT) and time-dependent DFT (TD-DFT). The results show that the properties of the dyes are sensitive to the N+ position in π-linkers. D series dyes with electron-withdrawing units located near the donor have better properties than the corresponding A series with the electron-withdrawing units located near the acceptor. For A and D series, the N+ modified dye named T2N+1-d displays the largest red shift of the UV-vis absorption, the maximum integral values of the adsorption-wavelength curves over the visible light, the highest light harvesting efficiency (LHE, 0.996), and the strongest adsorption energy (-44.33 kcal/mol). T2N+1-d also has a large driving force of hole injection (ΔGinj, -0.74 eV), which results in a more efficient hole injection. Bearing a lengthier π-linker than T2N+1-d, the properties of T2N+1-s are further improved. T2N+1-d moiety or its increased conjugated derivatives may be a promising π-linker.

Reactive molecular dynamics simulation of thermal decomposition for nano-aluminized explosives.

Aluminized explosives have important applications in civil construction and military armaments, but their thermal decomposition mechanisms are not well characterized. Here, the thermal decomposition of TNT, RDX, HMX and CL-20 on Al nanoparticles is examined by reactive dynamics simulations using a newly parameterized reactive force field with low gradient correction (ReaxFF-lg). Partially passivated Al nanoparticles were constructed and mixed with TNT, RDX, HMX and CL-20 crystals and then the mixed systems are heated to a high temperature in which the explosives are fully decomposed. The simulation results show that the aluminized explosives undergo three main steps of thermal decomposition, which were denoted "adsorption period" (0-20 ps), "diffusion period" (20-80 ps) and "formation period" (80-210 ps). These stages in sequence are the chemical adsorption between Al and surrounding explosive molecules (R-NO2-Al bonding), the decomposition of the explosives and the diffusion of O atoms into the Al nanoparticles, and the formation of final products. In the first stage, the Al nanoparticles decrease the decomposition reaction barriers of RDX (1.90 kJ g-1), HMX (1.95 kJ g-1) and CL-20 (1.18 kJ g-1), respectively, and decrease the decomposition reaction barrier of TNT from 2.99 to 0.29 kJ g-1. Comparing with the crystalline RDX, HMX and CL-20, the energy releases are increased by 4.73-4.96 kJ g-1 in the second stage. The number of produced H2O molecules increased by 25.27-27.81% and the number of CO2 molecules decreased by 47.73-68.01% in the third stage. These three stages are further confirmed by the evolutive diagram of the structure and temperature distribution for the CL-20/Al system. The onset temperatures (To) of generating H2O for all the aluminized explosives decrease, while those of generating CO2 for aluminized HMX and CL-20 increase, which are in accord with the experiment of aluminized RDX.

Molecular dynamic simulation for thermal decomposition of RDX with nano-AlH3 particles.

Molecular dynamic simulation of a high explosive, RDX, mixed with AlH3 nanoparticles was performed by a newly parameterized ReaxFF force field. Testing of the ReaxFF shows that the mean absolute errors of the densities and bond lengths between calculated and experimental values are less than 7% and 3%, respectively. Using the ReaxFF, effects of AlH3 nanoparticles with different radii on the thermal decomposition of RDX were revealed. A new mechanism of the generation and the consumption of H2 was discovered in the explosion. The H2 is released by AlH3 firstly and then it reacts with NO2 and CO2 from the decomposition of RDX, leading to an increase of H2O, NO and CO. Meanwhile, the size effect of AlH3 upon the reaction was also revealed. As a result, the number of produced H2O and CO2 molecules increases by 10.38% and 56.85%, respectively, when the radius of AlH3 nanoparticles decreases from 1.10 to 0.68 nm. This showed that RDX decomposes more completely with smaller AlH3 nanoparticles, which was further demonstrated by the analysis of reaction residues and diffusion coefficients.

Computational method on highly efficient D-π-A-π-D-based different molecular acceptors for organic solar cells applications and non-linear optical behaviour.

Eight molecular structures (BT-A1 to BT-A8) with high-performance non-fullerene acceptor (NFA) were selected for organic solar cells (OSCs) and non-linear optical (NLO) applications. Their electronic, photovoltaic (PV) and optoelectronic properties were tuned by adding powerful electron-withdrawing groups to the acceptor (A) of the D-π-A-π-D structure. Using time-dependent density functional theory (TD-DFT) techniques, based on the laws of quantum chemical calculations, the absorption spectra, stability of the highest and lowest-energy molecular orbitals (HOMO/LUMOs), electron density, intramolecular charge transfer (ICT), transition density matrix (TDM), were examined. The binding energy (Eb) and density of states (DOS) were probed to realize the optoelectronic analysis of the structures BT-A1 to BT-A8. Noncovalent interactions (NCIs) based on a reduced density gradient (RDG) were used to describe the nature and strength of D-A interactions in the molecules BT-A1 to BT-A8. The new refined molecules BT-A1 to BT-A8 exhibited strong absorbance bands between 408-721 nm and high electron transfer contribution (ETC) ranges between 87-96 %, along with the smallest excitation energies (Ex) between 1.71-3.55 eV in the solvent dichloromethane. Dipolar moment strengths ranging from 0.38 to 4.72 Debye in both the excited and ground states have determined with good solubility properties of BT-A1 to BT-A8 in polar solvent. Highly effective charge mobilities and prevention of charge recombination have been demonstrated by the electron (0.18-0.41 eV) and hole RE values (0.13-0.89 eV) for the new compounds. Power conversion efficiencies (PCE) of BT-A1 to BT-A8 were nearly the same because of better outcomes compared to the molecules in the BT. Compared to poly[4.8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b: 4,5-b']dithiophene-2,6- diyl-alt-(4-2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7-Th), the open circuit voltages (Voc) of compounds BT-A1 to BT-A8 were ranged from 1.52 to 2.13 eV. The polarizability (α) and hyperpolarizability (ß) of the molecules BT-A1 to BT-A8 were used to determine the non-linear optical (NLO) properties. The results showed that BT-A2, BT-A6 and BT-A7 have good NLO activity. This computational analysis demonstrates the superiority of the molecules with NFA. Hence the compounds are advised for the use in production of high-performance OSCs and NLO activity.

D-D-π-A organic dyes containing 4,4'-di(2-thienyl)triphenylamine moiety for efficient dye-sensitized solar cells.

Dye-sensitized solar cells (DSSCs) are currently under intense academic and industrial investigations, because of their environmentally-friendly, efficient, and low-cost features. The photosensitizer plays a key role in determining DSSCs' performance. The 4,4'-di(2-thienyl)triphenylamine moiety, included in dye TTC102, has been demonstrated before as a novel and efficient electron donor fragment. In this paper, the oversimple π-conjugated bridge of TTC102 was replaced by a 9-ethyl-3,6-di(2-thiophenyl)carbazole moiety. Two new D-D-π-A sensitizers, named TTC104 and TTC105, were synthesized and fully characterized. After anchoring on TiO(2) nanoparticle film, the absorption band of TTC104 is broader by 30 nm than that of TTC102. Under AM 1.5G irradiation, the energy conversion efficiency (η) of a DSSC based on TTC104 reaches 6.36%, which is 21.6% higher than that of TTC102 (5.24%). The results above demonstrate that the photovoltaic performance can be improved after introducing the 9-ethyl-3,6-di(2-thiophenyl)carbazole moiety to TTC102 when employed in DSSCs. Dye TTC105, containing a pyridyl group as the electron acceptor, showed only 1.88% conversion efficiency (η) when used in DSSCs. The huge different performances of TTC104 and TTC105 are proved to be partly due to the smaller dye loading amount, higher dark current and charge recombination rate of TTC105.

DFT studies on doping effect of Al12X: adsorption and dissociation of H2O on Al12X clusters.

The adsorption and reaction of H2O molecule on neutral X-centered icosahedronal Al12X clusters (X = Al, Mg, Zn, Ga, Ni, Fe, B, C, Si, P) were investigated by PW91, PBE, and PWC methods. Reaction energies and reaction barriers were determined. The spin states and the doped atoms have important influences on the Al12X geometries, density, electronic properties, and energy density of reaction between Al12X with a single H2O molecule. The energies of the neutral X-centered Al12X are lower than that of surface X-replaced Al12X with the exception of Al12Mg. The H2O dissociation on the Al12X (X = Mg, Zn, Ga, Ni, Fe) clusters have relatively low activation barriers, but large activation barriers for Al12X (X = B, C, Si, P). The activation barrier of water dissociation on the singlet Al12Fe cluster is the lowest, whereas the highest barrier is with the Al12C. The reaction of H2O with Al12Fe is the most exothermic. The center-Fe atom can move out to the surface after the adsorption and dissociation of H2O with an energy barrier of 172 kJ/mol. The results showed that the water dissociation on the Al12X cluster can be tuned by controllable X doping.

Adsorption of carbon dioxide on Al12X clusters studied by density functional theory: effect of charge and doping.

The adsorption of a CO2 molecule on neutral and charged X-centered icosahedron Al12X(±z) clusters (X = Al, Be, Zn, Ni, Cu, B, P; z = 0, 1) was investigated by the density functional PW91 and PWC methods. Optimized configurations corresponding to physisorption and chemisorption of CO2 were identified. The adsorption energies, activation barriers, and binding energies involving both the physisorption (Al12X(±z)·CO2-I) and chemisorption (Al12X(±z)·CO2-II) for CO2 were determined. The chemisorption of a CO2 molecule on the Al12X clusters (X is a metallic doping element) requires relatively low activation barriers. The lowest barrier was found to be with the Al12Be cluster. For the Al12X(-) clusters, the barriers are all higher than those of the neutral analogues. For the Al12X(+) clusters, two corresponding configurations are linked by a low-energy barrier, and CO2 molecule chemisorption on the Al12Be(+) cluster has the lowest barrier. The adsorption energies are larger than the energy barriers, which facilitates the chemisorption. The results show that carbon dioxide adsorbed on the Al12X(±z) clusters can be tuned by controllable X doping and the total number of valence electrons and suggest the potential application of Al12X(±z) nanostructures for carbon dioxide capture and activation.

Crystal morphology prediction of CL-20 and 1,4-DNI co-crystal at different temperatures.

CONTEXT: The morphologies of hexanitrohexaazaisowurtzitane (CL-20) and 1,4-dinitroimidazole (1,4-DNI) co-crystal under vacuum or solvent at different temperatures were predicted. The CL-20/1,4-DNI co-crystal has six important growth crystal planes: (002), (011), (101), (11‒1), (110), (111). The areas of (002), (101), and (011) planes account for a relatively large proportion, which are important crystal planes that affect the crystal morphology. The crystal habits at different temperatures were simulated. The simulation results showed that the crystal plane attachment energy of CL-20 and 1,4-DNI co-crystal increases with the increase of temperature, indicating that the increase of temperature is conducive to the growth of crystal planes. The aspect ratio decreases with the increase of temperature and the morphology of co-crystal becomes more spherical at a higher temperature. The theoretical predictions are in good agreement with the experiment. The simulation results can provide guidance for the crystallization of CL-20/1,4-DNI to obtain a nearly spherical crystal morphology. METHODS: The CL-20/1,4-DNI unit cell structure was geometrically optimized by the COMPASS force field. The AE model was used to predict the morphology of CL-20/1,4-DNI under vacuum, resulting in the most morphologically important growth planes. Ethyl acetate was selected as the solvent. The interaction energy between the solvent and the crystal plane, and the attachment energies in solvent at 298 K, 320 K, 340 K, 360 K, and 380 K were predicted. The NVT ensemble is used in the molecular dynamics calculation process. The simulation step is 1 fs and the total simulation time is 500 ps. The Andersen thermostat is selected as the temperature control method. In the potential energy calculation, the atom-based and Ewald methods were selected to calculate the van der Waals force and the electrostatic interaction force, respectively.

Theoretical design and evaluation of efficient small donor molecules for organic solar cells.

CONTEXT: The development of high-efficiency photovoltaic devices is the need of time with increasing demand for energy. Herein, we designed seven small molecule donors (SMDs) with A-π-D-π-A backbones containing various acceptor groups for high-efficiency organic solar cells (OSCs). Molecular engineering was performed by substituting the acceptor group in the synthesized compound (BPR) with another highly efficient acceptor group to improve the photoelectric performance of the molecule. METHOD: The photovoltaic, optoelectronic, and photophysical properties of the proposed compounds (BP1-BP7) were investigated in comparison to BPR using DFT and TD-DFT at MPW1PW91/6-311G(d,p) level of theory. All molecules we designed have red-shifted absorption spectra. The modification of the acceptor fragment of the BPR resulted in a reduced HOMO-LUMO energy gap; thus, the designed compounds (BP1-BP7) had improved optoelectronic responses as compared with the BPR molecule. Various key factors that are crucial for efficient SMDs such as exciton binding energy, frontier molecular orbitals (FMOs), absorption maximum (λmax), open circuit voltage (VOC), dipole moment (µ), excitation charge mobilities, and the transition density matrix of (BPR, BP1-BP7) have also been studied. Low reorganizational energy (holes and electrons) values provide high charge mobility, and all the designed compounds are efficient in this regard. Here, BP6 exhibits low excitation energy (1.66 eV), highest open circuit voltage (2.00 V), normalized VOC (77.23), and fill factor (0.931). Consequently, the superiority of the designed molecules advises experimenters to envision future developments in extremely effective OSC devices.

Facile synthesis of triazine-based microporous organic network for high-efficient adsorption of flumequine and nadifloxacin: A comprehensive study on adsorption mechanisms and practical application potentials.

Flumequine (FLU) and nadifloxacin (NAD), as emerging contaminants, have received extensive attention recently. In this study, a triazine-based microporous organic network (TMON) was synthetized and developed as an excellent adsorbent for FLU and NAD. The adsorption behavior and influence factors were investigated in both single and binary systems. Insight into the adsorption mechanisms were conducted through experiments, models, and computational studies, from macro and micro perspectives including functional groups, adsorption sites, adsorption energy and frontier molecular orbital. The results showed that the maximum adsorption capacities of TMON for FLU and NAD are 325.27 and 302.28 mg/g under 30 °C higher than records reported before. TMON exhibits the better adaptability and anti-interference ability for influence factors, leading to the preferable application effect in kinds of real water samples. TMON also shows the application potentials for the adsorption of other quinolone antibiotics and CO2 capture. Hydrogen-bonding interaction played the most critical role compared to π-π stacking effect, π-π electron-donor-acceptor interaction, CH-π interaction, and hydrophobic interaction during the adsorption. TMON could be regarded as a promising environmental adsorbent for its large surface area, stable physical and chemical properties, excellent recyclability, and wide range of applications.

Improvement of dye-sensitized solar cells' performance through introducing suitable heterocyclic groups to triarylamine dyes.

Dye-sensitized solar cells are currently under intense academic and industrial investigation, owing to their great potential to serve as a low-cost alternative to existing photovoltaic technologies. This paper puts forward a method, which adopts heterocyclic substituted triarylamine units as electronic donor moieties, to design triarylamine dyes for efficient dye-sensitized solar cells. Three novel triarylamine dyes named TTC101, TTC102 and TTC103, were synthesized economically through modification of the structure of a simple triarylamine dye (TC105) using three kinds of heterocyclic groups (4-pyridyl, 2-thienyl and 1-pyrazolyl). The crystal structure of TTC103 indicates that the heterocyclic groups would partly delocalize the positive charge after photooxidation. The overall solar-to-electrical energy conversion efficiencies (η) of TTC102 and TTC103 are 4.92% and 5.21% respectively under AM1.5G irradiation, reaching ∼82.3% and ∼77.7% of a N719-based reference cell under the same conditions. Besides, the energy conversion efficiencies (η) of TTC102 and TTC103 are 1.29 and 1.37 times the efficiency of TC105 respectively. All of the results above demonstrate that photovoltaic performance can be improved by introducing suitable heterocyclic groups to triarylamine dyes. A series of properties were investigated to explain the results, with a special emphasis on the geometric structures, energetics, and charge transfer processes at the dye/titania/electrolyte interface.

Nitrogen-rich polycyclic pentazolate salts as promising energetic materials: theoretical investigating.

Pentazolate (cyclo-N5-) salts are nitrogen-rich compounds with great development potential as energetic materials due to their full nitrogen anion. However, the densities of available N5- salts are generally low, which seriously lowers their performances. It is necessary to screen out cyclo-N5- salts with high density. To this end, eight new non-metallic cyclo-N5- salts based on fused heterocycle were designed. -NH2, -NO2, and -O- groups were introduced into the compounds to adjust and improve the detonation performance and impact sensitivity of cyclo-N5- salts. By theoretical calculations and Hirshfeld surface analyses, the densities, heats of formation, detonation performance, sensitivities, and crystal structures of the title compounds were predicted, and the contribution of hydrogen bond as well as π-π stacking to the stability of cyclo-N5- salt was revealed. The results indicate that the densities of title compounds are higher than 1.85 g cm‒3, and the sensitivities of these compounds are predicted to be lower than that of HMX. The detonation properties of a (D = 9.47 km s-1, P = 41.21 GPa) and d (D = 9.44 km s-1, P = 40.26 GPa) are better than those of HMX. These mean that using fused ring as a cation and introducing proper substituents are an effective method to improve cyclo-N5- salt's density and balance the detonation performance and sensitivity.

Theoretical research about nonmetallic energetic salts with pentazolate anion.

Significant progress has been made in the synthesis of nitrogen-rich high-energy salts by pairing pentazolate anion (cyclo-N5-) with different cations since cyclo-N5- was synthesized. It is difficult to screen out cyclo-N5- salts with high energy quickly and effectively in experiment, while theoretical research can realize this goal. Herein, nineteen high-energy salts, which were composed of tetrazole cation and cyclo-N5- anion, were designed. And their properties were studied via density functional theory and volume-based thermodynamic methods. The results indicate that most salts have high densities, low sensitivities, and good detonation properties. In particular, salt 14 (ρCalib = 1.802 g/cm3, ΔHf = 1058.4 kJ/mol, D = 9.38 km/s, P = 39.10 GPa, h50 = 44.92 cm) exhibits excellent detonation performance (approximating that of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20)) superior to 1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and lower impact sensitivity than CL-20 or HMX. Hence salt 14 is regarded as promising candidates for high-performance energetic materials.

Atomic perspective revealing for combustion evolution of nitromethane/nano-aluminum hydride composite.

Adding aluminum hydride (AlH3) into energetic materials (EMs) can improve their combustion and energy performance effectively. However, the potential mechanism of AlH3 on EMs is still unclear. Based on the ReaxFF-lg method, the thermal decomposition of nitromethane/nano-aluminum hydride (NM/nano-AlH3) composites were studied. The addition of AlH3 reduces the energy barrier and increases the energy release during the decomposition of NM, accelerates the decomposition of NM. The main way of AlH3 oxidation involves the capture of O atoms from NM. The results show that AlH3 content and passivated layer affect the oxidation and hydrogen release of AlH3. The explosion of small particle size AlH3 leads to rapid oxidation and hydrogen release. The oxidation of large particle size AlH3 is dominated by the inward and outward diffusion of O and Al atoms. The products of NM/nano-AlH3 composites are H2O, CO2, N2 gases, and Al clusters. This work is expected to guide the application of AlH3 in EMs.

Thermal Decomposition Mechanism of 1,3,5,7-Tetranitro-1,3,5,7-tetrazocane Accelerated by Nano-Aluminum Hydride (AlH3): ReaxFF-Lg Molecular Dynamics Simulation.

ReaxFF-low-gradient reactive force field with CHONAl parameters is used to simulate thermal decomposition of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) and AlH3 composite. Perfect AlH3 and surface-passivated AlH3 particles were constructed to mix with HMX. The simulation results indicate HMX is adsorbed on the surface of particles to form O-Al and N-Al bonds. The decomposition of HMX and AlH3 composite is an exothermic reaction without energy barrier, but the decomposition of pure HMX needs to overcome the energy barrier of 133.57 kcal/mol. Active nano-AlH3 causes HMX to decompose rapidly at low temperature, and the primary decomposition pathway is the rupture of N-O and C-N bonds. Adiabatic simulation shows that the energy release and temperature increase of HMX/AlH3 is much larger than those of the HMX system. Surface-passivated AlH3 particles only affect the initial decomposition rate of HMX. In HMX and AlH3 composites, the strong attraction of Al in AlH3 to O and the activation of the intermediate reaction by H2 cause HMX to decompose rapidly. The final decomposition products of pure HMX are H2O, N2, and CO2, and those of HMX/AlH3 are H2O, N2, and Al-containing clusters dominated by C-Al. The final gas production shows that the specific impulse of HMX/AlH3 is larger than that of HMX.