The following section first compares the DFT training data with the force field optimization results. In this context, we discuss the performance and limitations of the obtained ReaxFF parameters. We subsequently demonstrate the functionality of the force field by oxidizing a Mg nanoparticle in a GCMC simulation and then recrystallizing it into the thermodynamically stable rocksalt structure in a subsequent MD simulation. Afterwards, we simulate and discuss the first steps of Mg anode passivation. All fitted ReaxFF force field parameters for the Mg/O interactions are given in the Supporting Information.