A Study of the Shock Sensitivity of Energetic Single Crystals by Large-Scale Ab Initio Molecular Dynamics Simulations

Abstract

Understanding the reaction initiation of energetic single crystals under external stimuli is a long-term challenge in the field of high energy density materials. Herewith, we developed an ab initio molecular dynamics method based on the multiscale shock technique (MSST) and reported the reaction initiation mechanism by performing large-scale simulations for the sensitive explosive benzotrifuroxan (BTF), insensitive explosive triaminotrinitrobenzene (TATB), four polymorphs of hexanitrohexaazaisowurtzitane (CL-20) pristine crystals and five novel CL-20 cocrystals. A theoretical indicator, tinitiation, the delay of decomposition reaction under shock, was proposed to characterize the shock sensitivity of energetic single crystal, which was proved to be reliable and satisfactorily consistent with experiments. We found that it was the coupling of heat and pressure that drove the shock reaction, wherein the vibrational spectra, the specific heat capacity, as well as the strength of the trigger bonds were the determinants of the shock sensitivity. The intermolecular hydrogen bonds were found to effectively buffer the system from heating, thereby delaying the decomposition reaction and reducing the shock sensitivity of the energetic single crystal. Theoretical rules for synthesizing novel energetic materials with low shock sensitivity were given. Our work is expected to provide a useful reference for the understanding, certifying and adjusting of the shock sensitivity of novel energetic materials.

Strategies for Achieving Balance between Detonation Performance and Crystal Stability of High-Energy-Density Materials

“…Moreover, the compounds with neither HB nor p stacking present between the layers have their interlayer distance lying between the two, with an average d interlayer = 2.73 Å . This crystal packing rule is well consistent with the interspecies interactions mechanism that was revealed in our previous study (Zhang et al, 2019a(Zhang et al, , 2019b: HB is essentially a proton-lone pair attractive force and tends to decrease interlayer distance, whereas p-stacking interaction is lone pair-p exclusive and results in an increase in the interlayer distance. Figure 7F further confirms this mechanism and shows that HB interaction population plays a decisive role in regulating the LE of the HEDMs.…”

“…Figure 6A shows an obvious positive correlation between the measured thermostability and the calculated LE. Figure S9 also exhibits a general positive correlation between the mechanical sensitivity and the calculated LE (Zhang et al, 2019a(Zhang et al, , 2019b. Therefore, it is reasonable to employ LE as a theoretical indicator of crystal stability, which reflects the thermal and mechanical sensitivity of HEDMs.…”

“…As a result, the detonation performance parameters were calculated, directly on a crystal structural level, for all the 67 HEDMs in this study and are summarized in Table S2. The advantages of our theoretical calculations, over the traditional type of calculations, include the simultaneous consideration of the periodic crystal structure and the weak interactions among interspecies (Zhang et al, 2019a(Zhang et al, , 2019b. Therefore, the detonation performance parameters reported in this study are for the solid-state compounds instead of individual, gas phase molecules.…”

Applying machine learning to balance performance and stability of high energy density materials

“…For each of the studied 153 HEDMs, the compound name; its molecular formula, diagram, and conformation; as well as the Cambridge Crystallographic Data Center (CCDC) index number and Chemical Abstracts Service (CAS) number are provided in the Table S3 presented in the supplemental information . Details of our calculation methods of various physicochemical parameters and properties are described in our previous reports ( Zhang et al., 2016a , 2016b , 2019a , 2019b , 2019c , 2019d ; Jiang et al., 2018 ; He et al., 2017 ).…”

“…For example, hydrogen bonding (HB) plays a vital role in optimizing both detonation performance and crystal stability. Crystal structures of HEDMs rich in HBs were shown to have better stability, and expressed enhanced heat resistance and improved insensitivity to impact and shock stimuli , versus compounds with limited HB amount in their crystal structures ( Rupeng et al., 2019 ; Li et al., 2020a , 2020b , 2020c ; Zhang et al., 2019a , 2019b , 2019c , 2019d ). For example, when compared with neutral tetranitroamino HEDMs, corresponding energetic salts showed better thermal and mechanical stabilities, owing to the extensive HB interactions between cations and anions ( Lang et al., 2020 ).…”