Molecular dynamics simulation of TNT/ATL cocrystal morphology under different conditions

Molecular dynamics simulations were performed to investigate the growth morphology of TNT/ATL cocrystal (in a 1:1 M ratio) which is formed by the intermolecular interactions between ATL (1-amino-1,2,3-triazole, a new energetic material) and TNT (2,4,6-trinitrotoluene, a traditional explosive) in vacuum and various solvents. The attachment energies for four crystal planes (020, 011, 100, and 11 $\overline{1}$ ) and the morphological changes in six solvents (ethanol, acetonitrile, methanol, water, acetone, and ethyl acetate) at different temperatures were predicted. The results show that the aspect ratio of crystals grown in water, acetonitrile, and methanol solvents are smaller than in other solvents. While in ethanol, the predicted crystal morphology has a relative smaller aspect ratio of 4.60 at 318 K in comparison with other temperatures. The predicted results are highly consistent with the experiment. Furthermore, the solvent-crystal surface interactions and their influence on crystalline morphology were probed through solvent diffusion characteristics.

TNT/ATL cocrystal morphologies in vacuum and different solvents and temperatures were obtained by COMPASS force field and MAE (modified attachment energy) model, which considers the direct impact of intermolecular interactions on crystal morphology via the molecular dynamics simulation at Materials Studio 7.0 platform. The geometry optimization using fine precision with a 1.55-nm cutoff distance was performed with Forcite module, incorporating Ewald summation for electrostatic interactions and atomic-based summation for van der Waals forces. Comprehensive crystal morphology predictions were performed through the Morphology module, utilizing three distinct algorithms: growth morphology, BFDH (Bravais-Friedel-Donnay-Harker), and equilibrium morphology methodologies. The BFDH model predicts crystal growth using geometric calculations based on the symmetry of the crystal and lattice parameters. The NVT (isothermal and isochoric) system was used for molecular dynamics simulation. The simulation step size was 1 fs, the total simulation time was 500 ps, and data were collected every 5000 steps.