TDDFT calculations of the PETN's ultraviolet absorption spectrum under the electric field loading.

CONTEXT: The UV(ultraviolet) absorption spectrum of PETN under different electric field loading directions(X, Y, and Z) with the value of strength range from 0.001 a.u. to 0.006 a.u. was calculated with the TDDFT(Time-dependent density functional) in this work. With the increase of electric field strength, the absorbance of PETN in the ultraviolet band decreases. To explain the action mechanism of the electric field on PETN UV(ultraviolet) absorption spectrum, we analyzed and counted the contribution rate, oscillator strength, and vertical excitation energy of the main excitation process whose contribution rate to the UV absorption spectrum is greater than 10%. The contribution of PETN to the UV spectrum in all directions without an electric field was also listed to investigate the anisotropy of PETN in the excitation process under an electric field. The hole-electron analysis showed that the electric field will enhance the charge transfer characteristics in the excitation process of PETN. To investigate the anisotropy of the response under different electric field application directions, the contribution of the UV absorption spectrum in different directions was studied. METHODS: Optimization and TDDFT calculation were performed at the level of M06-2X/def2-TZVP and PBE0/def2-TZVP respectively, with Gaussian09 program. The hole-electron analysis and UV absorption spectrum plotting were performed with Multiwfn3.8.

Effect of solvent mixture on the formation of CL-20/HMX cocrystal explosives.

2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20)/1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX) cocrystal is widely concerned due to its high safety and low sensitivity. A CL-20/HMX-solution interface model was constructed to investigate the effect of solvent mixture on cocrystal morphology. The interface models of different solvent mixtures were simulated by molecular dynamics (MD) and quantum chemistry (QC) methods at room temperature. The analyses of binding energy show that CL-20 and HMX molecules are easier to be adsorbed on the cocrystal surface in the presence of solvent mixture dimethyl sulfoxide (DMSO)/acetonitrile (ACN). Mass density distribution and diffusion coefficient analyses demonstrated that the growth of CL-20/HMX cocrystal will be freer in DMSO/ACN. Cooperativity effect analysis shows that the CL-20 binding to HMX is tighter in the presence of DMSO/ACN and the system is more stable. Our findings may provide some guidelines for preparing cocrystal in solvent mixture. Graphical abstract.

Theoretical and experimental investigation into a eutectic system of 3,4-dinitropyrazole and 1-methyl-3,4,5-trinitropyrazole.

Eutectic mixtures of 3,4-dinitropyrazole (DNP) and 1-methyl-3,4,5-trinitropyrazole (MTNP) were investigated by theoretical and experimental methods. The mass ratio of DNP and MTNP ranged from 0:100 to 100:0. Melting points of the mixtures were predicted through observing the inflection point of a specific volume vs. temperature in molecular dynamics (MD) simulation. The results are in good agreement with experimental results obtained from the differential scanning calorimeter (DSC) study. The binding energy of a 50/50 DNP/MTNP eutectic mixture is lower than those of other mixtures, in accordance with the common sense that the melting point of materials is linked to the strength of intermolecular interactions. There are definitely hydrogen bonds and dispersion interactions between DNP and MTNP based on the analyses of interaction energy, atom in molecules (AIM), and reduced density gradient (RDG). The eutectic mixture would be encouraged to be used in melt-cast explosives because of the favorable sensitivity to heat and impact, great detonation performances, acceptable vacuum stability and excellent compatibility with high explosives. Graphical abstract The eutectic mixture of DNP and MTNP were investigated through molecular dynamics (MD) simulation and quantum chemistry calculations. The predicted melting points of mixtures are in good agreement with the experimental data. The eutectic mixture shows good stability.

Growth morphology of CL-20/HMX cocrystal explosive: insights from solvent behavior under different temperatures.

A 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) /1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX)-isopropanol (IPA) interfacial model was constructed to investigate the effect of temperature on cocrystal morphology. A constant volume and temperature molecular dynamics (NVT-MD) simulation was performed on the interfacial model at various temperatures (295-355 K, 20 K intervals). The surface electrostatic potential (ESP) of the CL-20/HMX cocrystal structure and IPA molecule were studied by the B3LYP method at 6-311++G (d, p) level. The surface energies, polarities, adsorption energy, mass density distribution, radial distribution function (RDF), mean square displacement (MSD) and relative changes of attachment energy were analyzed. The results show that polarities of (1 0 0) and (0 1 1) cocrystal surfaces may be more negative and affected by IPA solvent. The adsorption energy per area indicates that growth of the (1 0-2) face in IPA conditions may be more limited, while the (1 0 0) face tends to grow more freely. MSD and diffusion coefficient (D) analyses demonstrated that IPA molecules gather more easily on the cocrystal surface at lower temperatures, and hence have a larger effect on the growth of cocrystal faces. RDF analysis shows that, with the increasing of temperature, the strength of hydrogen bond interactions between cocrystal and solvent becomes stronger, being highest at 335 K for the (1 0 0) and (0 1 1) interfacial models. Results of relative changes of modified attachment energy show that (1 0 0) and (0 1 1) faces tends to be larger than other faces. Moreover, the predicted morphologies at 295 and 355 K are consistent with experimental values, proving that the CL-20/HMX-IPA interfacial model is a reasonable one for this study. Graphical Abstract Construction of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) /1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX)-isopropanol (IPA) interfacial model, analysis, and morphology prediction of cocrystal.

Theoretical investigation of the effects of the molar ratio and solvent on the formation of the pyrazole-nitroamine cocrystal explosive 3,4-dinitropyrazole (DNP)/2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20).

The effects of the molar ratio, temperature, and solvent on the formation of the cocrystal explosive DNP/CL-20 were investigated using molecular dynamics (MD) simulation. The cocrystal structure was predicted through Monte Carlo (MC) simulation and using first-principles methods. The results showed that the DNP/CL-20 cocrystal might be more stable in the molar ratio 1:1 near to 318 K, and the most probable cocrystal crystallizes in the triclinic crystal system with the space group P[Formula: see text]. Cocrystallization was more likely to occur in methanol and ethanol at 308 K as a result of solvent effects. The optimized structure and the reduced density gradient (RDG) of the DNP/CL-20 complex confirmed that the main driving forces for cocrystallization were a series of hydrogen bonds and van der Waals forces. Analyses of the trigger bonds, the charges on the nitro groups, the electrostatic surface potential (ESP), and the free space per molecule in the cocrystal lattice were carried out to further explore their influences on the sensitivity of CL-20. The results indicated that the DNP/CL-20 complex tended to be more stable and insensitive than pure CL-20. Moreover, an investigation of the detonation performance of the DNP/CL-20 cocrystal indicated that it possesses high power. Graphical abstract DNP/CL-20 cocrystal models with different molar ratios were investigated at different temperatures using molecular dynamics (MD) simulation methods. Binding energies and mechanical properties were probed to determine the stability and performance of each cocrystal model. Solvated DNP/CL-20 models were established by adding solvent molecules to the cocrystal surface. The binding energies of the models in various solvents were calculated in order to identify the most suitable solvent and temperature for preparing the cocrystal explosive DNP/CL-20.

Theoretical insight into the binding energy and detonation performance of ε-, γ-, ß-CL-20 cocrystals with ß-HMX, FOX-7, and DMF in different molar ratios, as well as electrostatic potential.

Molecular dynamics method was employed to study the binding energies on the selected crystal planes of the ε-, γ-, ß-conformation 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (ε-, γ-, ß-CL-20) cocrystal explosives with 1,1-diamino-2,2-dinitroethylene (FOX-7), 1,3,5,7-tetranitro- 1,3,5,7-tetrazacyclooctane with ß-conformation (ß-HMX) and N,N-dimethylformamide (DMF) in different molar ratios. The oxygen balance, density, detonation velocity, detonation pressure, and surface electrostatic potential were analyzed. The results indicate that the binding energies E b (*) and stabilities are in the order of 1:1 > 2:1 > 3:1 > 5:1 > 8:1 (CL-20:FOX-7/ß-HMX/DMF). The values of E b (*) and stabilities of the energetic-nonenergetic CL-20/DMF cocrystals are far larger than those of the energetic-energetic CL-20/FOX-7 and CL-20/ß-HMX, and those of CL-20/ß-HMX are the smallest. For CL-20/FOX-7 and CL-20/ß-HMX, the largest E b (*) appears in the cocrystals with the 1:1, 1:2 or 1:3 molar ratio, and the stabilities of the cocrystals with the excess ratio of CL-20 are weaker than those in the cocrystals with the excess ratio of FOX-7 or ß-HMX. In CL-20/FOX-7, CL-20 prefers adopting the γ-form, and ε-CL-20 is the preference in CL-20/ß-HMX, and ε-CL-20 and ß-CL-20 can be found in CL-20/DMF. The CL-20/FOX-7 and CL-20/ß-HMX cocrystals with low molar ratios can meet the requirements of low sensitive high energetic materials. Surface electrostatic potential reveals the nature of the sensitivity change upon the cocrystal formation. Graphical Abstract MD method was employed to study the binding energies on the selected crystal planes in the ε-, γ-, ß-CL-20 cocrystals with FOX-7, ß-HMX and DMF in different molar ratios. Surface electrostatic potential reveals the nature of the sensitivity change in cocrystals.

Theoretical insight into the sensitive mechanism of multilayer-shaped cocrystal explosives: compression and slide.

Multilayer-shaped compression and slide models were employed to investigate the complex sensitive mechanisms of cocrystal explosives in response to external mechanical stimuli. Here, density functional theory (DFT) calculations implementing the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE) with the Tkatchenko-Scheffler (TS) dispersion correction were applied to a series of cocrystal explosives: diacetone diperoxide (DADP)/1,3,5-trichloro-2,4,6-trinitrobenzene (TCTNB), DADP/1,3,5-tribromo-2,4,6-trinitrobenzene (TBTNB) and DADP/1,3,5-triiodo-2,4,6-trinitrobenzene (TITNB). The results show that the GGA-PBE-TS method is suitable for calculating these cocrystal systems. Compression and slide models illustrate well the sensitive mechanism of layer-shaped cocrystals of DADP/TCTNB and DADP/TITNB, in accordance with the results from electrostatic potentials and free space per molecule in cocrystal lattice analyses. DADP/TCTNB and DADP/TBTNB prefer sliding along a diagonal direction on the a-c face and generating strong intermolecular repulsions, compared to DADP/TITNB, which slides parallel to the b-c face. The impact sensitivity of DADP/TBTNB is predicted to be the same as that of DADP/TCTNB, and the impact sensitivity of DADP/TBTNB may be slightly more insensitive than that of DADP and much more sensitive than that of TBTNB.