The automated reaction mechanisms and kinetics (AutoMeKin) program evolved from transition state search using chemical dynamics simulations (TSSCDS). It combines a series of empirical, semi-empirical and ab initio calculation methods...

To improve the transition state (TS) search capability in complex chemical environments, AMK_Mountain is constructed based on the automated reaction mechanisms and kinetics (AutoMeKin) package. AMK_Mountain does not distinguish the reaction type of the TSs, which is beneficial to obtaining a more comprehensive reaction mechanism. In this study, the first step of the alkaline hydrolysis process of nitrocellulose monomer was adopted as the research object, and 730 possible initial configurations are constructed and 22 TSs pass high‐level calculations. Energy difference and interaction region indicator reveal that the first step of alkaline hydrolysis is mainly the combination of nitrogen‐containing functional groups at the positions α and β with hydroxide anions, followed by the formation of nitric acid and the further loss of protons to form nitrate. Overall, in combination with GFN2‐xTB and ORCA, the AMK_Mountain technique provides a reliable method for the location of the TSs in complex environments.

The reactive force field (ReaxFF) molecular dynamics simulation is an effective method to study the behavior of energetic materials in the aqueous phase. In order to optimize the ReaxFF of energetic materials in the aqueous phase, we have developed a multiple objective nondominated sorting genetic algorithm II (NSGA-II)-based optimization program (MONOP). The MONOP was used by adopting the CHON-2017_weak as the initial force field to re-optimize the force field of a 2,4,6trinitrotoluene (TNT)/water system. In addition, the ReaxFF-lg (low-gradient dispersion correction), CHON-2017_weak, and TNT/water were used to simulate TNT crystals correspondingly. Ultimately, the TNT diffusion coefficient in the aqueous phase was also calculated by the mean squared displacement (MSD) method. The optimization results showed that the MONOP optimization has a fast global convergence, in about 11 generations in this study. By comparing the lattice constants a, b, c, density, and the radial distribution functions of the TNT element pairs, the TNT/water system was found to describe TNT crystals well. Relatively, the TNT/water system had a slightly larger value of liquid water density than that of the experimental measurement. The MSD results showed that the migration rate of TNT molecules in water is much slower than that of OH anions in water; thus, it is reasonable to conclude that the TNT hydrolysis reaction is dominated by OH anions attacking TNT molecules, and the reaction mostly occurs at the liquid−solid interface. This study indicates that the MONOP optimizes the ReaxFF and has broad application prospects; the diffusion coefficient of TNT in water can provide theoretical support for the aqueous phase degradation of energetic materials.

The alkaline hydrolysis reaction of energetic materials is important and complex. With improved performance, AMK_Mountain was used to systematically study the alkaline hydrolysis of the nitrocellulose monomer and hexogen. The reaction pathways showed that the nitrocellulose monomer produces the nitrate anion and nitrite anion differently, while hexogen only produces the nitrite anion. Electronic structure results at the M06-2X/6-311G(d,p)/PCM(Pauling) level showed that the nitrocellulose monomer and hexogen have a similar pathway in their main energy-releasing process (nitrite anion production): with electrostatic attraction effects after proton transfer, the nitrite anion dissociates from the original structure with a low barrier. Moreover, during the alkaline hydrolysis of the nitrocellulose monomer, the metastable intermediates after proton transfer may be directly generated following transition states that, structurally, tend to produce nitrite anions “proximal” to the proton transfer site and produce nitrate anions “distal” to the proton transfer site. Electronic structure analysis showed that representative metastable intermediates revealed that the charge transfer caused by electrostatic attraction may be the direct cause of these reactions.

As an organic molecule catalyst, N,N',N"‐trihydroxyisocyanuric acid can selectively catalyze the oxidation of the methyl group of waste 2,4,6‐trinitrotoluene to generate 2,4,6‐trinitrobenzoic acid. This reaction can avoid environmental pollution by inorganic heavy metal catalysts. In this study, four reaction stages of this catalytic reaction were designed and validated computationally at the M06‐2X‐D3ZERO/6‐311G(d,p) level using the acetic acid solvent model. These validations include transition state searches, intrinsic reaction coordinate calculations, reactant and product optimizations, and frequency calculations. The final reaction network of 23 transition states shows that after N,N',N"‐trihydroxyisocyanuric acid activation and common reaction, the network bifurcates into two stages: alcohol to carboxylic acid and aldehyde to carboxylic acid. Although the former stage releases about 155 kcal/mol of Gibbs free energy, less than the 177 kcal/mol from the latter stage, the overall reaction equation shows that the pathway including former stage does not consume the catalytically active substance IM_T2, which saves the energy required for reactivation and is thus more favorable. Furthermore, the key transition states in the reaction network include bimolecular substitution reactions and proton hopping transfer reactions. Analyses of their interaction region indicators and intrinsic reaction coordinate results demonstrate strong selectivity. Additionally, the energy barriers and heat releases of the latter are twice and 1.3 times greater than those of the former, respectively. In summary, this study elucidated two competitive reaction pathways and identified the more energetically favorable and selective pathway, it provides useful insights for further optimization of industrial utilization of 2,4,6‐trinitrotoluene.