Theoretical Simulations On The Structure And Properties Of HMX Based Crystals

Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine(HMX)is one of the most powerful explosive with excellent comprehensive performance.It has been widely used in military weapon like the propellants,warhead and polymer-bonded explosives(PBXs).In the field of energetic materials,the sensitivity and safety is a very complicated but crucial topic.And the safety mechanism depends on the structures characteristics,properties and external stimulation styles,In the present work,we choose HMX with prominent performance as our research objective.By using the method of molecular dynamics(MD)simulation and quantum chemistry(density functional theory,DFT),we studied the structures and properties of three single crystal of HMX(?-??-and ?-HMX)and HMX/LLM-105 co-crystal.And we systematically studied the formation mechanism of HMX/LLM-105.In order to fully understand the response laws of HMX to environmental stimulus,the sensitivity,stability and mechanical energy of HMX was investigate under different pressures and temperatures.Through the exploration of morphologies for HMX and LLM-105 and their interface behavior,the growth mechanism of HMX/ LLM-105 cocrystal system was revealed.Hoping our researches can provide overall understanding of HMX,put forward an effective way to reduce the sensitivity of HMX,improve the performance of HMX,and expand its application scope.Finally,the main findings are summarized as follows:1?Based on density functional theory,the geometrical structures of?-HMX under the hydrostatic pressure of 0 GPa ?12GPa were investigated on the GGA/PBE level.And it is found that the crystal densities increase with the increment of pressure.Indicating that compressing is a promising method to improve the detonation performance.The compressibility of ?-HMX are different in three directions.It is more easily to compressed along the direction of axis a and b.Finally,the electronic characteristics analysis under hydrostatic pressure indicate that sensitivity and stability of ?-HMX decrease with pressure increasing.2?Molecular dynamics(MD)simulation and COMPASS force field are used to research the influence of temperature on ?-HMX??-HMX and ?/?-HMX complex(2:1).The calculated physical parameters such as bond length,cohesive energy density(CED),and mechanical parameters are consistent,all indicate that the sensitivities increase and stabilities decrease when temperature rises.The mixed system is obviously inferior to the than single crystal.Moreover,the mechanical performance of ?/?-HMX will be further damaged when the temperature is higher than 373 K.3?The morphologies of HMX and LLM-105 are predicted by the attachment energy(AE)model in vacuum and the predicted morphologically dominant crystal habits are(011),(11-1),(020),(100),(10-2)and(011),(020),(110),(10-1),(11-1),(101)for HMX and LLM-105 respectively;6 interface structures of HMX and LLM-105 are constructed.DFT and NPT-MD simulations have been performed to research their properties and the cocrystal mechanism.We discoveries that the order of interaction strength of HMX crystal surface with LLM-105 surface is as follows:(11-1)/(110)>(011)/(110)>(11-1)/(020)>(11-1)/(011)>(011)/(011)>(011)/(020)(?>?>?>?>?>?);Strong vd W interactions and hydrogen bonds existence in all of the interface structures except(011)/(020)interface(?);The hydrogen-bonded interactions in the interfaces mainly originate from O of HMX and H of LLM-105 or inverse,and the non-bonded interactions in(11-1)/(110)interface(?)are the strongest;Additionally,calculated electrostatic properties indicates that(11-1)face of HMX blend tightly with the(110)face of LLM-105,while the interaction in(011)/(020)model is the weakest;(11-1)/(110)interface(?)contribute to the formation of HMX/LLM-105 cocrystal.This structure exerts superior mechanical properties.This paper,multiple modern simulation methods are applied to enrich the understanding of different HMX crystal types and the cocrystal mechanism of HMX/LLM-105 is well explored.Hoping that our research may contribute to the preparation of HMX/ LLM-105.Our work will provide a theoretical reference to explore other high-performance of HMX-based cocrystals and expand HMX's application scope.