Theoretical Studies On Molecular Design,Intermolecular Interactions,and Decomposition Mechanisms Of Cage And Cocrystal Explosives

Energetic materials are widely used in many fields of civil and military.As an important national strategic energy,synthesizing high-energy density compounds（HEDCs）has always been research focus and hotspots at home and abroad.In this dissertation,the molecular design,intermolecular interactions and decomposition mechanisms of cage and cocrystal explosives were systematically studied through theoretical calculations and simulations.The main contents of the dissertation are as follows:1.Molecular design of azabicyclo[3.1.1]heptane derivativesBased on the basic skeleton of bicyclo[3.1.1]heptane,two azabicyclo[3.1.1]heptanes（A and B）were built by substituting its tertiary carbon atoms using nitrogen atoms.One or two N-O groups were introduced into A and B to build three azabicyclo[3.1.1]heptane oxides（A1,B1,and B2）.Azabicyclo[3.1.1]heptane derivatives were obtained by substituting different hydrogen atoms of B2 using nitro groups.Their geometry,heats of formation,detonation performance,and impact sensitivity were systematically studied using density functional theory（DFT）.According to the combination standard of detonation performance and stability,B2-3NO₂was obtained as a potential candidate for HEDCs.2.Molecular design of cage 7-nitro-1,4,7-triazabicyclo[2.2.1]heptane derivativesA new skeleton 7-nitro-1,4,7-triazabicyclo[2.2.1]heptane was firstly designed.Then,the energetic groups such as-C（R2）-,-N（R）-and-O-（R=H,NO₂,or NH₂）were chosen as intramolecular linkages rather than substituents to build a series of new cage compounds A,B,C,D,E,and F.Three novel cage compounds were generated by properly introducing-N（R）-linkages in the molecular structure of the cage compounds A,B,and D,which were named as G,H,and I.Their geometry,energy gaps,heats of formation,detonation performance and impact sensitivity were systematically studied by DFT.According to the combination standard of detonation performance and stability,A2,B3,C2 and G3 were selected as potential candidates for HEDCs.3.Molecular design and intermolecular interactions of cage RDX and HMX derivativesBased on the molecular skeletons of 1,3,5-trinitro-1,3,5-triazinane（RDX）and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane（HMX）,a series of cage compounds were designed by using different numbers of-N（NO₂）-and-N（NH₂）-to connect the two skeletons of RDX or HMX to construct the cage frameworks.Their electronic structure,heats of formation,detonation performances,and impact sensitivity were systematically studied by DFT,screening out TR2,TR3,TH2 and TH4 can be considered as potential candidates for HEDCs.Then,the interactions between bimolecules were studied by reduced density gradient analysis and electron density difference analysis,and their effects on the impact sensitivity of explosives were obtained.4.Molecular design,intermolecular interactions,and decomposition mechanisms of bicyclic and cage RDX derivativesA series of new high-energy insensitive compounds were designed based on RDX skeleton through incorporating-N（NO₂）-CH₂-N（NO₂）-,-N（NH₂）-,-N（NO₂）-,and-O-linkages.Then,their electronic structures,heats of formation,detonation properties and impact sensitivities were analyzed and predicted using DFT,all designed compounds can be considered as potential candidates for HEDCs.Then,by calculating the interaction energy,topological analysis of electron density,reduced density gradient analysis and electron density difference analysis,it is found that R3 is the most stable.The decomposition process of best performing R3 crystal at 2500 K was simulated by ab initio molecular dynamics（AIMD）,and found that there are 4 initial reaction mechanisms and 2 subsequent decomposition reactions.Through a series of ring opening and reorganization,the reaction is gradually broken to form small molecules.5.Performance,intermolecular interactions,and decomposition mechanisms of cocrystal explosive DAF:ADNPThe crystal density,detonation performance,and impact sensitivity of 3,4-diaminofurazan（DAF）:4-amino-3,5-dinitropyrazole（ADNP）cocrystal were studied by DFT.Compared with the pure crystals,the detonation performance of the DAF:ADNP cocrystal slightly decreases,but its impact sensitivity obviously decreases.Then,the intermolecular interactions in the cocrystal were studied.The results indicate that thatπ-πstacking and strong H···N interactions obviously increase intralayer molecular interactions and reduce its impact sensitivity.The decomposition process of the DAF:ADNP cocrystal at different temperatures（2400-3000 K）were simulated by density functional tight-binding molecular dynamics（DFTB-MD）method.There are four different initiation mechanisms were obtained and kinetic parameters were obtained by first-order reaction rate model fitting.6.Performance,intermolecular interactions,and decomposition mechanisms of CL-20-based cocrystal explosivesThe performance and intermolecular interactions of the cocrystals CL-20（2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane）:DNP（2,4-dinitro-2,4-diazapentane）and CL-20:DNG（2,4-dinitro-2,4-diazaheptane）were comparatively studied by DFT.Compared with the pure CL-20 crystal,the detonation performance of the cocrystals CL-20:DNP and CL-20:DNG slightly decrease,but their impact sensitivity obviously decrease.The strong hydrogen bonding and vd W interactions in the cocrystals greatly increase intralayer molecular interactions and reduce their impact sensitivity.The decomposition process of the two cocrystals at different temperatures（1000,2000 and 3000 K）and high temperature coupled with high pressures（2000 K and 1-5 GPa）were simulated by DFTB-MD method.The main initial,subsequent decomposition mechanisms and decomposition products of CL-20,DNP and DNG molecules were obtained.