Predicting the Morphology of β-HMX Crystal using Molecular Dynamics Study

The growth habit of β-HMX crystals grown from acetone has been characterized with (020), (011), (110) and (101) faces both from experimental and theoretical studies. In the present work, this growth habit is elucidated with the spiral growth mechanism, which is the dominant growth mechanism at low supersaturations. For the external habit controlling factors in the model, we suggest a generalized interfacial structure analysis model to account for the effects of both the anisotropic local concentrations of the growth units at the interface and the free energy barriers for reorientation of the growth units. In order to compute the free energy surfaces, we used metadynamics with molecular order parameters as the collective variables to identify the orientation and conformation of the adsorbed growth unit. The predicted morphology of β-HMX through our approach implies the significance of the role of anisotropic local concentrations on the relative growth rates of the slow growing faces.