Multiple Objective NSGA-II-Based Optimization Program and Its Application in Reactive Force Field for 2,4,6-Trinitrotoluene Diffusion in the Aqueous Phase

Abstract

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.

Heuristic-Based Alkaline Hydrolysis Mechanism of Nitrate Ester (Nitrocellulose Monomer) and Nitroamine (Hexogen) Compounds: Electrostatic Attraction Effect of the Nitro Group

“…], and nitroamine compounds [RDX, 1,3,5,7-tetranitro-1,3,5,7-tetrazolidine (HMX), hexanitrohexaazaisowurtzitane (CL-20), etc.]. For the aromatic energetic materials represented by TNT, the π bond of the benzene ring has a strong attraction to hydroxide anions, so bimolecular substitution reactions tend to occur in such materials and then generate nitrite anions. ,,− The heat of such reactions is approximately 3 times the energy barrier. For the nitrate ester compounds represented by NC, experiments have shown that the alkaline hydrolysis reactions do not open rings until all nitrogen-containing groups are eliminated and simultaneously produce nitrate anions and nitrite anions. ,,, There is a great challenge of transition state (TS) analysis to clearly elucidate these reaction results. ,, For the nitramine compounds represented by RDX, the process of producing nitrite anions and the process of proton transfer belong to the same TS .…”

On the Design and Optimization of a Clean and Efficient Combustion Mode for Internal Combustion Engines through a Computer NSGA-II Algorithm

“…In recent years, genetic algorithms have been widely used in the optimization design of internal combustion engines. Among them, (Non-dominated Sorting Genetic Algorithm (NSGA)-II has obvious advantages in convergence speed and optimization results [6]. Jin et al [7] optimized the NSGA-II so that the gasoline/diesel RCCI can cover a larger operating load with higher fuel economy and lower exhaust emissions, but the engine is sensitive to initial conditions and boundary conditions, and corresponding measures need to be taken to guarantee the stability of its operation.…”