Development of a ReaxFF reactive force-field modeling for magnesium nanoparticles and water system
Yong Zhang, Zheng Mei, Fang-Chao Hou, Xiaohong Wu, Yun-Hui Hou, Min Li, Jing Sun, Liang Song
Abstract
The Mg/O/H ReaxFF force field was developed based on the JAX-ReaxFF framework of the gradient descent algorithm to elucidate the intricate interactions and hydrogen production mechanisms of Mg nanoparticles and H 2 O. The ReaxFF parameters were optimized based on a quantum mechanical training set, which included the interactions between Mg/O/H, as well as the equation of state of MgH 2 and Mg(OH) 2 crystals. Molecular dynamics simulations were conducted to simulate the structural evolution of Mg nanoparticles in an H 2 O atmosphere at high temperatures. Results show that H 2 O dissociates on the surface of Mg nanoparticles to form Mg-H, Mg-OH, and Mg-O bonds. Structural evolutions of Mg nanoparticles depend on the temperature and the density of H 2 O. The inward diffusion rate of H atoms surpasses that of O atoms, resulting in the formation of a Mg hydride core and a Mg oxide shell. Chemical bond analysis demonstrates a correlation between H 2 production and H 2 O consumption, with H 2 production trailing H 2 O consumption. The inward diffusion of O atoms and the outward diffusion of Mg atoms lead to the release of H 2 from the magnesium hydride. The ReaxFF protocol stands as a valuable tool for studying the hydrogen production in magnesium-water systems at the atomic level.