Optimization and Application of ReaxFF for the Aqueous Carbonation of Calcium Silicates in Steel Slag

Abstract The existing ReaxFF for the C/H/O/Ca/Si system exhibits poor compatibility with aqueous multiphase reactions. In this work, the aqueous carbonation of dicalcium silicate (C2S) derived from steel slag was selected as the research system, and parameter optimization and validation of the reactive force field were performed. Density functional theory with the GGA-PBE functional was adopted to conduct structural relaxation and potential energy surface scanning for C2S polymorphs, carbonate species, and reaction intermediates, and a comprehensive structure-energy training data set was established. Subsequently, ReaxFF parameters were trained using the ParAMS module, and molecular dynamics simulations of aqueous C2S carbonation were implemented via the LAMMPS code. The results show that the equation-of-state curves (volume-energy, bond length-energy, etc.) of the optimized C/H/O/Ca/Si force field agree well with the DFT reference data, which effectively addresses the difficulty in characterizing multiphase interfacial reactions involving water molecules. This optimized force field was applied to 10 ns MD simulations for the aqueous carbonation of β-C2S and γ-C2S. The simulations successfully reproduced the efficient adsorption and accumulation of CO2 and H2O on the C2S surface, while maintaining favorable computational efficiency with conventional computing resources. The force field parameters obtained in this study provide a robust computational tool for further elucidating the microscopic mechanism of aqueous carbon sequestration by calcium silicates.