•Reaction will start when the initial distance among participating reactants is shorter than the minimum initial distance of reaction that initiates reaction initialization through excellent physical interfacial contact.•2D distribution binning in the xy plane and the average bond length analysis based on ReaxFF MD trajectories reveal reaction characteristics and iron aluminides products.Compared with organic-counterpart or micro-counterpart, nanothermites have attracted substantial interests owing to their exhibited outstanding properties. A common goal of a great amount of studies in nanothermite-based energetic materials is to enhance the reaction properties. Thermite planar geometry structural systems have been the promising structures because they are very tunable to control the alternating layered geometry and thickness of fuel and oxidizer. In this article, the planar interfacial contact Al/Fe2O3 nanolaminate thermite systems were studied to explore the effects of variations in preheating temperature, preheating rate and the initial distance between participating fuel and oxidizer on reaction properties and products characterizations by using the classic molecular dynamics simulations. According to the results, ignition delay and reaction time decrease with increasing the preheating temperature. The ignition delay and reaction time decrease from hundreds of picoseconds to a few tens of picoseconds. Additionally, higher heating rate results in higher energized structure, and much more energy was absorbed during heating period leading to a much shorter ignition delay. Reaction will start when the initial distance among reactants is shorter than a certain distance after passing through the ignition delay. Analyses also show the majority number of triangular structure for Fe2Al clusters and a small amount of tetrahedral structure for Fe3Al clusters during thermite reaction.

Using density functional theory, we investigated the hydrogen storage capacity of Li coated BC3 honeycomb sheet. Our result indicates 18 H2 molecules can be adsorbed on BC3Li6 complex with a storage gravimetric density of 9.68 wt% and the average adsorption energy reaches 0.206 eV/H2. This is desirable for absorbing and desorbing H2 molecules at near ambient conditions.

The thermophysical properties of the liquid oxygen and nitrogen (O2–N2) mixture under extreme conditions are studied by quantum molecular dynamic (QMD) simulations based on van der Waals (vdW) density-functional theory (DFT-D). We have calculated the principal Hugoniots of the O2–N2 mixture both with and without explicit treatment of spin, and obtained good agreement with shock experiments along the first shock Hugoniot. The Hugoniot is not significantly sensitive to the spin effects, while the key role of spin effect on the structural properties is found. When density and pressure increase, the O2–N2 mixture is observed to undergo a continuous transition. The dissociation, recombination of N2 and O2 molecules, and formation of products, such as NO, NO2, NO3, and N2O, along the Hugoniot have been predicted by means of pair-correlation functions (PCFs), and the configuration evolution of the system is also discussed. We find the decomposition of N2 molecules occurs at much a lower temperature and pressure (4000 K, 19 GPa) than those for pure liquid nitrogen. With the continuous increase of density and temperature, the formation of polymeric structures is observed. To study the Mott transition, we calculate the electronic density of states (DOS) of the O2–N2 mixture along the 500 K isotherm and the transformation from a semiconducting to a metallic fluid occurs at the pressure approaching 36 GPa, where the liquid mixture consists entirely of stable molecules.

•The electric field intensity can affect the melting temperature.•The time required for the collapse of the structure strongly depends on the electric field.•The applied electric fields result in significant changes in the electronic structures.In this paper, molecular dynamics simulations are carried out to study the melting process of the β-crystobalite structure under the effect of various electric fields. The results reveal that the higher electric field contributes to the damage of the β-crystobalite. Meanwhile, the applied electric field can affect the damage process of β-crystobalite, especially the melting temperature. And the melting point reduces as the strength of the electric field is increased. It is also found that the time required for the collapse of the structure strongly depends on the electric field. In addition, the presence of external electric fields results in significant changes in the electronic structures. It can be seen that there are noticeable changes in the shape of the density of states (DOS) curves.

•The best basis set is the aug-cc-pV5Z for O and the cc-pCV5Z for Ca and the active space is chosen for 4220.•The comprehensive line intensities are computed for X1Σ+ 1-0, 2-1, 3-2, 4-3, 2-0, 3-1, and 4-2 bands.•The transition dipole moment A1Σ+–X1Σ+ and line intensities for A1Σ+(v = 0)–X1Σ+(v = 0) band are firstly calculated.Highly correlated ab initio calculations were performed for accurate determination of the lowest two 1Σ+ states of CaO molecule. Highly accurate multi-reference configuration interaction (MRCI) approach and active space (4220) were used to investigate the potential energy curves (PECs) and dipole moment curves (DMCs) of X1Σ+ and A1Σ+ states. The PECs of the two states agree well with Rydberg–Klein–Rees (RKR) potential. Computations were performed using aug-cc-pV5Z basis set for O and cc-pCVnZ for Ca. Partition function was calculated using two different methods to obtain the spectral absolute intensity from 100 K to 1000 K. Moreover, the ro-vibrational transition dipole moments and Einstein A coefficient were calculated to predict the line lists of ro-vibrational spectral intensities. The line lists of the X1Σ+ included 1-0, 2-1, 3-2, 4-3, 2-0, 3-1, and 4-2 bands. This study is the first to calculate the transition dipole moment of A1Σ+–X1Σ+ and line intensities of 1-0 band.

•The (S, Nb)-codoping induces lattice distortion and reduces the recombination of photo-generated electron–hole pairs.•The synergistic effect of (S, Nb)-codoped system further reduces band gap due to a S 2p and Nb 4d state appears in the gap.•The (S, Nb)-codoping should be grown under Ti-rich conditions while S or Nb mono-doping is expected to be easier under O-rich conditions.•The calculated results would be beneficial to further developing for titanium dioxide photocatalyst.The geometrical structure, defect formation, electronic and optical properties of S-doped, Nb-doped, and (S, Nb)-codoped anatase TiO2 were successfully calculated by the first-principles plane-wave ultrasoft pseudopotential method based on the density functional theory with plus U method. Firstly, the geometrical structure demonstrates that the (S, Nb) co-doping can effectively induce lattice distortion and reduce the recombination of electron–hole pairs. Note that the (S, Nb)-codoped system further reduces the band gap compared with pure and mono-doped TiO2 due to the mixture of S 2p and Nb 4d states appears in the gap, which results in an obvious red-shift in the optical absorption spectra and improves the photocatalytic activity. Moreover, the (S, Nb) co-doping should be grown under Ti-rich conditions while S or Nb mono-doping is expected to be easier under O-rich conditions. The above results would be beneficial to further developing for titanium dioxide photocatalyst.

•Pillared graphene bubble system is used for the first time in this paper.•These systems are systematically calculated using MD method in the NPT ensemble.•The maximum gravimetric and volumetric H2 densities of the developed systems are calculated – 21.3 wt% and 210.3 kg/m3.The storage of molecular hydrogen in a novel 3D carbon structure – pillared graphene bubble system under various environments is calculated using molecular dynamics (MD) method. The graphene-based structures are designed with different sizes of semi-ellipsoidal graphene bubbles. The effects of pressure, temperature, and graphene interlayer spacing are systematically investigated in the isothermal–isobaric (NPT) ensemble. Meanwhile, the internal pressures of molecular hydrogen in bubbles under various environments are also estimated. Results show that the hydrogen storage capacity of the pillared graphene bubble structures can be maximized by decreasing the temperature and increasing the pressure and the graphene interlayer spacing. The MD simulations demonstrate that the maximum gravimetric and volumetric H2 densities inside the developed system are 13.7 wt% and 121.6 kg/m3, respectively. Impressively, the maximum gravimetric and volumetric H2 densities of the developed system are also calculated – 21.3 wt% and 210.3 kg/m3, respectively, when the outer surface adsorption are taken into consideration. These values satisfy the requirements for mobile applications set by the U.S. Department of Energy (DOE).

In this paper, we designed a new type of 3D graphene bubble structure for hydrogen storage in theory. The graphene-based structures are constructed with different sizes of semi-ellipsoidal graphene bubbles. The hydrogen storage efficiency of the graphene bubble structures at ambient conditions (P = 1.0 bar and T = 300 K) is calculated using molecular dynamic (MD) simulations. The effects of number of graphene layers and density and size of bubbles are systematically investigated in the isothermal–isobaric (NPT) ensemble. The MD results reveal that at ambient conditions, the bubble models can achieve the highest volumetric hydrogen storage efficiency of ~45 kg/m3 and gravimetric hydrogen storage efficiency of ~3.75 wt%. The maximum pressures in the bubbles are also evaluated.

•The adsorbed R can lead to the structural changes in the Al core.•The Al cluster is conducive to the dissociation of the nitro group.•Most of the interactions are exothermic processes.In this paper, we investigate the interaction between Aln (n = 5, 6) cluster and small molecules. Our study shows that the Al cluster promotes the dissociation of the nitro group, while the adsorbed R can lead to the changes in Al core structures. In addition, the fact that Al atom tends to attach to O atom is also observed, if the adsorbed molecules contain O atom. What’s more, the introduction of O atom might eventually break the Al–Al bond with the formation of the Al–O–Al bond, and drive the system to a lower energy state. According to the calculated heats of formation, all of the interactions are exothermic processes, except for the interaction between CH2O and Al5.Graphical abstract

•The EDMF was first directly fitted for the spin-orbit splitting of nitric oxide.•Ab initio EDMF is more close to three fitting ones than the previous theoretical one.•The vibrational transition moments agree well with experiments at large overtone.•The calculated line intensities agree well with measurements.An accurate electric dipole moment function (EDMF) has been obtained by fitting the best available data including the pure rotational band 0–0 for individual ro-vibrational transitions for nitric oxide. Line intensities calculated using the fitted EDMF agree better with the measurements than the current HITRAN database. Moreover, the accurate ab initio potential energy curve (PEC) and EDMF were found using the multi-reference averaged quadratic coupled-cluster (AQCC) approach with the basis set aug-cc-pV6Z (aV6Z). The good agreement of the vibrational transition moments, computed using the Rydberg–Klein–Rees (RKR) potential and the fitted EDMFs, with experiments shows the present fitted EDMF could be more accurate than other fitted ones at the valid range. Our ab initio vibrational transition moments agree better with experimental data than the ones calculated using the previous theoretical PEC and EDMF, especially at the high overtones. We expect that the present study will be helpful for the transitions including high υ and high overtone bands of NO.

First-principles pseudopotential calculations are performed to investigate the phase transition and elastic properties of niobium nitrides (NbN). The lattice parameters a0 and c0/a0, elastic constants Cij, bulk modulus B0, and the pressure derivative of bulk modulus B0′ are calculated. The results are in good agreement with numerous experimental and theoretical data. The enthalpy calculations predict that NbN undergoes phase transition from NaCl-type to NiAs-type structure at 13.4 GPa with a volume collapse of about 4.0% and from AsNi-type to CW-type structure at 26.5 GPa with a volume collapse of about 7.0%. Among the four types of structures, CW-type is the most stable structure. The elastic properties are analyzed on the basis of the calculated elastic constants. Isotropic wave velocities and anisotropic elasticity of NbN are studied in detail. The longitudinal and shear-wave velocities, VP, VS and Vm increase with increasing pressure, respectively. The Debye temperature ΘD increases monotonically with increasing pressure except for NiAs-type structure. Both the longitudinal velocity and the shear-wave velocity increase with pressure for wave vector along all the propagation directions, except for VTA([100]) and VTA[001]([110]) with NaCl structure and VTA[010]([100]) with the other three types of structures.

•Transient absorption and luminescence spectra at sub-damage site of K9 glass by laser irradiation at 355 nm are presented.•As the energy density increases to 2.54 J/cm2, the absorption intensity reaches to about 0.2.•The mechanism of two-photon ionization mainly plays a critical role at sub-damage site.•Intensity of Raman spectra is very high at low energy density and decreased with respect to high energy density.Transient absorption and luminescence spectra at sub-damage site of K9 glass by laser irradiation at 355 nm are presented. The dependence of transient absorption on laser energy and number of pulses was investigated. As the energy density increases to 2.54 and 3.18 J/cm2, the transient absorption intensity reaches to about 0.20 range from 400 to 480 nm. With the increase of number of pulses the process of residual absorption appears, which can be used to explain the fatigue effect of K9 glass. The defects in K9 glass were investigated by fluorescence and Raman spectra. The fluorescence band centered at about 410 nm is attributed to oxygen deficiency centers. The mechanism of two-photon ionization plays a critical role at sub-damage site. Compared to the Raman spectra of pristine site, intensity of Raman spectra is very high at a lower energy density, while it decreased at a higher energy density.

In order to explore the damage mechanisms of K9 glass irradiated by high energy density ultraviolet laser, laser-induced fluorescence and Raman spectra were investigated. Compared the fluorescence spectra of damaged area, undamaged area and sub-damaged area, it can be conclude that the fluorescence spectrum of sub-damaged area is different from the structure of the other two areas. Especially, the main peak of the spectra at 415 nm reveals the unique characteristics of K9 glass. The structure at the sub-damaged area enhances intensity of the Raman scattering spectra. Three peaks of the spectra at about 500 nm and two characteristic peaks at about 550 nm exhibit the characterization of damaged area. A peak of the Raman scattering spectra at 350 nm which related to water can be observed. The relationship between intensity of Raman scattering and laser intensity at 355 nm is investigated by confocal Raman microscopy. At sub-damage area, signal of Raman scattering is rather high and decreased dramatically with respect to energy density. The major band at about 1470 cm−1 sharpened and moved to higher frequency with densification. These phenomena demonstrate that the structure of sub-damaged area has some characterization compared with the damaged area. The investigation of defect induced fluorescence and Raman spectra on surface of K9 glass is important to explore the damage mechanisms of optical materials irradiated by ultraviolet laser irradiation at 355 nm.

The electronic structure of CaB2O4(III) crystal obtained by using SIESTA program is reported in this article. It is observed that the band gap values are, respectively, 5.39 and 5.89 eV from our LDA and GGA calculations. The bond covalency and bond valence are calculated with a simplified method. For both Ca–O and B–O types of bond, the bond covalency has a decreasing trend with the increasing bond length. The result of bond covalency in explaining the interaction between atoms has been shown in good agreement with that of Mulliken population analysis. The ionic configuration for CaB2O4(III) in the fundamental state is estimated to be Ca+1.808B−0.68O−0.112. A summary of B–O distances for the four phases of CaB2O4 crystal from several works is also presented.

Density functional theory has been used to investigate geometries, C–NO2 bond dissociation energies (BDEs), heats of formation (HOFs), and relative specific impulses (Is) of 2,4,5-trinitroimidazole and its three derivatives (1-methyl-2,4,5-trinitroimidazole (I), 1-carboethoxy-2,4,5-trinitroimidazole (II) and 1-picryl-2,4,5-trinitroimidazole (III)). The trigger linkage C–NO2 in process of detonation has been identified on basis of bond dissociation energies. Heats of formation in gas phase at 298 K are determined for the first time using working chemical reactions at B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) level. The performance of our employed theoretical level and reactions for calculating HOFs is first verified to be accurate to within 1 kcal mol−1 by a test system. Then HOFs are computed to be 48.1, 52.2 ± 0.6, −35.7 ± 0.9 and 105.7 ± 0.7 kcal mol−1 for 2,4,5-trinitroimidazole, compounds I, II, and III, respectively. Based on the calculated values of HOFs and Is, we predict III to be a good candidate for high energy material.

Because secondary explosives are stable molecules with large energy barriers to chemical reaction, in shock or impact initiation, a sizable amount of phonon energy must be converted to the molecular internal higher vibrations by multiphonon up pumping. To investigate the relationship between impact sensitivities and energy transfer rate, the number of doorway modes of explosives is estimated by a simple theory in which the rate is proportional to the number of normal mode vibrations. We evaluated frequencies of normal mode vibrations of 2,4,6-trinitro-m-cresol (C7H5N3O7), picric acid, TNB, TNAP, TNT, TNA, TBN, DATB, and TATB by means of density functional theory (DFT) at the b3p86/6-31g (d,p) level. The number of doorway modes in the regions of 200–700 cm−1 was evaluated by the direct counting method. It is found that the number of doorway modes shows a linearly correlation to the impact sensitivities derived from drop hammer tests. This result is in agreement with several previous works. Besides, it is also noted in our study that in those secondary explosives with similar molecular structure and similar molecular weight, the correlation between the impact sensitivity and the number of doorway modes is very high.

In this paper, quantum chemical calculations are used to estimate C–NO2 bond dissociation energies (BDE) for 16 chain nitro compounds. These compounds are studied by employing four hybrid density functional theory (B3LYP, B3PW91, B3P86 and PBE1PBE) methods in conjunction with the 6-31G∗, 6-311G∗ and 6-311++G∗∗ basis sets, and at the same time, the complete basis set CBS-QB3 method is also performed. The obtained results are compared with the available experimental values. It is demonstrated that the B3LYP and B3PW91 methods are not suitable for our nitro compounds system, while B3P86 method is able to give reliable BDE data. The results show that P3P86 together with 6-31G∗ is also better than CBS-QB3 method for most of molecules. So we can see that the B3P86 method may be more suitable to produce reasonable BDE of C–NO2 bond for chain nitro compounds. In order to know if the rule is fit to the ring nitro compounds, two molecules have been calculated. The result is not consistent with the former.

The equilibrium structure of the compound Li8Al3Si5 has been obtained via the minimization of the total energy within local spin density approximation (LSDA) based on density functional theory (DFT). The calculated lattice constant and bond length are in good agreement with available experimental values, and the phonon band structure is also described. In the meantime, the thermodynamic properties are investigated applying Debye model combining with the first principle theory in the quasi-harmonic approximation. The evaluated lattice constant and bulk modulus using this model both well agree with the values from ab intio and from the experiment. Our results demonstrate that this method can provide reliable predictions for the temperature and pressure dependence of these quantities, such as the equation of state, the bulk modulus, the Debye temperature, the heat capacity and the thermal expansion in detail.

Bond dissociation energies for removal of the nitrogen dioxide moiety in nitrobenzene; 3-amino-nitrobenze; 4-amino-nitrobenze; 1,3-dinitrobenzene; 1,4-dinitrobenzene; 2-methyl-nitrobenzene; 4-methyl-nitrobenzene; and 1,3,5-trinitrobenzene nitroaromatic molecules, are calculated using the three hybrid density functional theory (B3LYP, B3PW91, B3P86) methods with 6-311G** and 6-31+G** basis sets. By comparing the computed energies and experimental results, it is find that the B3LYP and B3PW91 methods are unable to predict satisfactory results of bond dissociation energy (BDE), however, the B3P86 method is able to give the best agreement with experimental BDE data for these nitroaromatic molecules, especially with 6-311G** basis set.

•The line intensities of the five bands of N2 are computed for the first time.•The calculated TDMCs are more reasonable than the results of other studies.•Our calculated Einstein A coefficients are consistent with the experiment results.•The CASSCF/MRCI/aVQZ method with 3110311 can well depict the N2(A-B).The absolute absorption spectral line intensities of the 0-0, 1-1, 2-2, 3-3, and 4-4 bands of N2(A3Σu+ − B3Пg) are computed for the first time with the accurate potential energy curves (PECs) and transition dipole moment curves (TDMCs) using the ab initio calculation. During the calculation process, the precise multireference configuration interaction (MRCI) approach with the augmented correlation consistent polarized valence quadruple-zeta set (aug-cc-pVQZ) and active space 3110311 are used. The calculated PECs of the two states (A3Σu+, B3Пg) agree well with Rydberg-Klein-Rees (RKR) potential, and the calculated TDMCs are more reasonable than the results of other studies. Our calculated Einstein A coefficients are also well consistent with the recent experiment results. The intensities of five bands are obtained from the summation of their respective absolute line intensities, for instance, the 0-0 band intensities are 3.25 × 10−16 cm−1/(molecule cm−2) at 300 K and 1.65 × 10−16 cm−1/(molecule cm−2) at 3000 K. The theoretical results are credible. They are also beneficial for astrophysics where high temperature dominates.The absolute line intensities and positions for the 0-0 band of N2(A-B).

•The (S, Nb)-codoping induces lattice distortion and reduces the recombination of photo-generated electron–hole pairs.•The synergistic effect of (S, Nb)-codoped system further reduces band gap due to a S 2p and Nb 4d state appears in the gap.•The (S, Nb)-codoping should be grown under Ti-rich conditions while S or Nb mono-doping is expected to be easier under O-rich conditions.•The calculated results would be beneficial to further developing for titanium dioxide photocatalyst.The geometrical structure, defect formation, electronic and optical properties of S-doped, Nb-doped, and (S, Nb)-codoped anatase TiO2 were successfully calculated by the first-principles plane-wave ultrasoft pseudopotential method based on the density functional theory with plus U method. Firstly, the geometrical structure demonstrates that the (S, Nb) co-doping can effectively induce lattice distortion and reduce the recombination of electron–hole pairs. Note that the (S, Nb)-codoped system further reduces the band gap compared with pure and mono-doped TiO2 due to the mixture of S 2p and Nb 4d states appears in the gap, which results in an obvious red-shift in the optical absorption spectra and improves the photocatalytic activity. Moreover, the (S, Nb) co-doping should be grown under Ti-rich conditions while S or Nb mono-doping is expected to be easier under O-rich conditions. The above results would be beneficial to further developing for titanium dioxide photocatalyst.

•We studied the hydrogen storage capacity of Li12F12 nano-cage.•The adsorption energy is good for the storage and release of the H2 molecules.•Li12F12 nano-cage will become a promising storage medium in the future.We use the first-principles calculation based on density functional theory (DFT) to investigate the hydrogen storage on Li12F12 nano-cage. Our result indicates the largest hydrogen gravimetric density is 7.14 wt% and this is higher than the 2017 target from the US department of energy (DOE). Meanwhile, the average adsorption energy is −0.161 eV/H2, which is desirable for absorbing and desorbing H2 molecules at near ambient conditions. These findings will have important implications on designing hydrogen storage materials in the future.