The cocrystal mechanism of HMX and LLM-105 by theoretical simulations

Abstract

Isothermal-isobaric molecular dynamics (NPT-MD) simulations and density functional theory (DFT) calculations were performed to explore the cocrystal formation mechanism of energetic materials. Based on the morphologically dominant crystal habits of HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) and LLM-105 (2,6-diamino-3,5-dinitropyrazine-l-oxide), six interface structures of HMX with LLM-105 have been established to obtain the interaction energy, radial distribution function (RDF), electrostatic potential and mechanical properties. It revealed that the interaction energies in different models are different, owing to the various molecular orientation and stackingmanner of the contacted crystal face of HMX and LLM-105. The (1 1 –1)/(1 1 0) interface is mainly governed by the O···H hydrogen bond and strong van der Waals forces and this model possesses the largest interaction energy. Electrostatic potentials indicate (1 1 –1)/(1 1 0) interface blending the strongest, which reveals that the cocrystal process is stronglyrelevant to the interface behavior of (1 1 –1)/(1 1 0) among the 6 interfaces. Moreover, the mechanical parameters show that the (1 1 –1)/(1 1 0) interface structure (VI) exhibits excellent ductility and fracture strength. Additionally, this work presents a novel insight, which from the crystal face of HMX and LLM-105 as well as the interaction behavior to research the cocrystal mechanism.