Sequential Molecular Dynamics Simulations: A Strategy for Complex Chemical Reactions and a Case Study on the Graphitization of Cooked 1,3,5-Triamino-2,4,6-trinitrobenzene

Abstract

The fundamental core of chemistry is to create new substances, and numerous complex reactions may be involved in chemical conversions. Nevertheless, clarifying the mechanisms of these complex reactions remains challenging, thereby causing insufficiencies in the fundamentals to guide new substance creation. This work proposes and emphasizes a strategy of sequential molecular dynamics simulations (SMDSs) toward complex chemical reactions. The strategy is successfully demonstrated by clarifying a complex graphitization process of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), whose mechanism has not been imaged by a single simulation alone. We conducted SMDSs with a molecular reactive force field, ReaxFF, to resemble the cook-off of TATB, i.e., a sequence of heating, expansion, and cooling acting on TATB. Graphitization is found to sequentially undergo TATB molecular decay, clustering, cluster enlargement to C sheets (sheeting), and layered stacking of C sheets, along with phase separation. Moreover, the structures graphitized from TATB can be imaged only when simulations are conducted in the sequence of heating, expansion, and cooling, in accordance with the actual conditions of cooking TATB. This successful exemplification shows that a large number of complex reaction mechanisms can be revealed using the SMDS strategy and computation ability promotion, in combination with the clarified experimental conditions. This strategy exhibits considerable potential for future use.

Influence of Al and Al2O3 Nanoparticles on the Thermal Decay of 1,3,5-Trinitro-1,3,5-triazinane (RDX): Reactive Molecular Dynamics Simulations

“…However, this setup that is very common among ReaxFF-MD simulations has been confirmed to be feasible to reflect reaction mechansim. [46][47][48][49] Besides, for convenience, we define R as the ratio of the number of a chemical species to that of RDX to analyze reaction mechanism. Notably, 1500 K is the closest to the temperature adopted in the experiment, below 1000 K. 14,17,23,50 Therefore, the present result agrees with that the high activity of nano Al has frequently been shown to catalyze the thermal decomposition of RDX.…”

Molecular Forcefield Methods for Describing Energetic Molecular Crystals: A Review

“… where D e σ , D e π , and D e ππ are the bond parameters for σ-bonds, π-bonds, and π-π bonds, respectively; p be 1 and p be 2 are the fitting parameters. ReaxFF [ 98 , 99 , 100 ] was initially developed for simulating combustion of hydrocarbon and reactions of energetic compounds, and the functional groups such as nitro group are well-parameterized, thus various energetic compounds such as RDX, HMX, CL-20, PETN, NM, TNT, TATB, and TATP were applied [ 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 , 134 , 135 , 136 ]. The ReaxFF-based MD simulations provide an efficient way to investigate the chemical reactions and other properties of various molecular crystals under particular conditions.…”

“…Another important aspect of the application of ReaxFF-MD is to disclose thermal decomposition mechanism under various heating conditions, with evolution of the gas products, key reactions, and kinetics detailed [ 132 , 133 , 134 , 135 , 136 ]. ReaxFF-MD has been utilized to compare the thermal reactivity for perfect and imperfect energetic crystals.…”

“…For example, Deng et al [ 132 ] used ReaxFF-MD to compare the thermal decay of perfect and twinned β-HMX under constant-temperature, programmed, and adiabatic heating conditions, and it was found that enhanced self-heating ability stems from the high internal energy of the molecules around the defects. ReaxFF-MD has also been applied to compare the initial cluster evolution for insensitive TATB, relatively sensitive β-HMX, and sensitive PETN under heating conditions—and a correlation was established between OB and clustering [ 133 , 134 ]. Moreover, it was used to understand the mediated thermal stability of the cocrystal of CL-20/HMX, compared with the pure components [ 135 ].…”

Dissociative adsorption modes of TATB on the Al (111) surface: a DFT investigation

“…Thus, signicant experimental and theoretical investigations have been focused on TATB. [7][8][9] Numerous investigations have been focused on its thermal decomposition and structural details, and several possibilities have been introduced for the decomposition pathways of TATB; however, the universal mechanism of these reactions is still unknown.…”