As initial test cases we applied the trained Mg/O potential in two subsequent GCMC simulations to investigate the thermodynamic oxidation behavior of a Mg nanoparticle. Therefore, we started with a clean, equilibrium-shaped Mg 978 nanoparticle and inserted in the first GCMC simulation oxygen atoms up to an O/Mg ratio of 1.0. As shown in Figure , oxygen is mainly inserted at the particle's surface during early stages of the simulation. Note that especially oct sites are populated first and that the surface starts to reshape into the rocksalt structure. Upon reaching an O/Mg ratio of 1.0, the particle is not yet fully oxidized to the core -as shown in the cross-section of the particle images in Figure -but a series of non-dissociated O 2 molecules is adsorbed on the surface. As the simulation continues, the surface is covered with more and more O 2 molecules but complete oxidation to the core was not achieved even after 10 000 iterations (see Figure ). Thus, to accelerate the process, we decided to perform a second GCMC simulation, using a nanoparticle with an O/Mg ratio of 1.0 as the input structure from the first GCMC simulation. In 20 000 additional iterations, we allowed only O-move steps but prohibited further oxygen atoms from being inserted or removed. As a result, now oxygen diffusion processes lead to oxidation of the particle's core.