Prediction of Growth Habit of β-Cyclotetramethylene-tetranitramine Crystals by the First-Principles Models

Abstract

Experimentally, β-cyclotetramethylene-tetranitramine (β-HMX) crystals were found to dramatically elongate to the [100] direction when a relatively high supersaturation was imposed. A sudden growth of β-HMX to the [100] direction is closely associated with a mechanistic transition from spiral growth to two-dimensional (2D) nucleation for the (110) face. The onset supersaturation for the growth by 2D nucleation, σ 2D , was found to play a key role in the growth of β-HMX. The present simulation results based on first-principles models such as the spiral growth model and the 2D nucleation model show that the values of σ 2D on the (101) and (101̅ ) faces are smaller than those on the (020), (110), and (011) faces. This leads to the prediction of rapid growth rates for the (101) and (101̅ ) faces by 2D nucleation at low supersaturation and the appearance of a typical shape of β-HMX. On the other hand, the needle-like shape of β-HMX begins to prevail when the supersaturation exceeds the σ 2D for the (110) face because its growth mechanism is transformed from the spiral growth mechanism to the 2D nucleation mechanism which accompanies rapid growth of the (110) face. As a result, the present predictions are in remarkable agreement with the experiments. Furthermore, the kinetic Monte Carlo (KMC) simulation also shows that the σ 2D for the (110) face is lower than that for the (011) face because the (011) face provides the surface topology on which growth units are unfavorably incorporated into the lattice sites. It evidently shows that the relative positions of σ 2D bring on the advent of needle-like growth of β-HMX.

A design aid for crystal growth engineering

“…This model accounts for the non-isotropic behavior of complex organic molecules and performs well at predicting the growth habit of pharmaceutical molecules; it has recently been adopted outside of our group for various crystalline explosives, with successful results also [15][16][17]. Central to the model are calculations of the net rates of solute attachment into kink sites on spiral edges, from which the normal growth rate of each face results.…”

Understanding the growth morphology of explosive crystals in solution: insights from solvent behavior at the crystal surface

“…In recent years, many approaches based on computational simulations have been employed to dissect the morphology resulting from the growth mechanism of an explosive crystal from a microscopic point of view, including the Bravais, Friedel, Donnay, and Harker (BFDH) rules, [3][4][5] the attached energy model and its modication, [6][7][8][9][10][11][12][13][14] the occupancy model, 15 Monte Carlo simulation, 16,17 the spiral growth model, and the 2D nucleation model. [18][19][20] These methods evolved from geometry, energy, and mechanistic models, and extend the breadth of knowledge about the factors that inuence the crystal morphology, ranging from the gas phase, the solvent medium, the temperature, and the additive to supersaturation, which helps researchers interpret and design crystallization experiments. While most studies have been focused on the prediction of an explosive crystal's morphology in solution, understanding of the solvent behavior and the interfacial interaction for the growth morphology of explosive crystals at the molecular level still remain inadequate.…”

Molecular dynamics simulation on the morphology of 1,1-diamino-2,2-dinitroethylene (FOX-7) affected by dimethyl sulfoxide (DMSO) and temperature

“…Temperature is one of the factors that affects the morphology of crystals. 8 We have performed MD simulations to explain the relationship between the FOX-7 morphology and temperature in DMSO solvent. Table 6 and Fig.…”

“…The morphology of explosive is governed by both the internal structure and the external D r a f t conditions such as solvent 5 , temperature, additive and crystal technology 6 , among which solvent and temperature have been found to be critical external factors determining the relative growth rate and consequently the crystal habit 7,8 .…”