We used the GCMC algorithm implemented in the AMS driver program, 56 originally developed by Senftle et al. as an extension for standalone ReaxFF. In a T V µ O N Mg ensemble, the algorithm randomly decides whether an oxygen atom should be (1) inserted, (2) removed, or (3) displaced in the system. The coordinates for the insertion and displacement steps are chosen randomly. The algorithm places atoms further than 1.85 Å to the nearest atom to prevent a Coulomb collapse (excessive Coulomb attraction) but closer than 3.0 Å to achieve faster convergence. Subsequently, the system's geometry is relaxed until the norms of all forces were less than 0.1 eV Å-1 or the maximum number of steps (1000) was reached. Finally, the following probabilities decide whether the executed Monte Carlo (MC) step is accepted or rejected: