Molecular Dynamics Simulation on Crystal Morphology of LLM-105

To study the crystal growth morphology of 2, 6-diamino-3, 5-dinitropyrazine-1-oxide (LLM-105) under the condition of vacuum or solvent dimethyl sulfoxide (DMSO), the double layer structure model of LLM-105 in DMSO solvent was constructed by the molecular dynamics simulation method. The equilibrium morphology method and crystal growth morphology were used to predict the crystal morphology of LLM-105 in vacuum. The main control crystal surface and its growth rate of LLM-105 in DMSO environment were analyzed by modified attachment energy. The interaction between different crystal surfaces and DMSO was analyzed by radial distribution function and surface structure.The nucleation energy barrier of LLM-105 particles was analyzed. The results show that four main growth surfaces of LLM-105 crystal are (0 1 1), (0 2 0), (1 1 0) and (1 0 -1), of which, (0 2 0) and (0 1 1) crystal surfaces are the controlled crystal surfaces. After adding solvent DMSO, the modified attachment energy is analyzed to find that the attachment energy of four crystal surfaces in solvent is far smaller than that in the vacuum condition. It is suggested that the appropriate polar solvent can help to suppress explosive nucleation and control the morphology of LLM-105 crystal, of which the linear growth rate of (0 1 1) crystal surface is the smallest. The analyses of radial distribution function and crystal surface structure show that there are strong hydrogen bond and van der Waals interactions between H atoms of DMSO and N atoms of LLM-105 (0 1 1) surface. The analysis of diffusion coefficient shows that, the modified attachment energy decreases with the increase of solvent diffusion coefficient, and the maximum diffusion coefficient of solvent DMSO on (0 1 1) crystal surface is observed, which results in the high nucleation barrier of (0 1 1) surface and not easy to aggregate nucleation.