Molecular-dynamic simulation of isotherm of cyclotetramethylenetranetramine with the nanopore type defect

Molecular dynamic simulation of isothermal compression parameters are performed for a cyclotetramethylenetetranitramine single crystal (C₄H₈N₈O₈, HMX) using a modified ReaxFF-lg reactive force field. The unit cell consisted of eight C₄H₈N₈O₈ molecules (144 atoms). The calculated supercell consisted of an optimized unit cell and was created with a periodicity of 6×6×6 (48384 atoms). Our calculations were performed for the pressure range of 1–40 GPa, and the state of the single crystal C₄H₈N₈O₈ under the conditions of P = 0.05 GPa and T = 300 K was chosen as the initial state. The calculated isotherm of the material is consistent with experimental data. Static compression calculations of molecular crystal C₄H₈N₈O₈ with the nanopore type defect were carried out to study the effect of defects on the compressibility of crystals. Nanopores two sizes were considered. By results of calculations it was performed that the material with nanopore type defect is deformed more strongly, and the greater the defect, the stronger the deformation. At the same pressure value, the nanopore crystal has a higher compression ratio than an ideal single crystal. (paper)