1. We perform hybrid Monte Carlo-Molecular Dynamics (MC-MD) simulations in the grand canonical ensemble using the LAMMPS software. We use a Pt/O/H/C/Ni ReaxFF forcefield developed by Gai et al., which is originally based on a forcefield from Fantauzzi et al. This forcefield has been previously used in studies focusing on the oxidation of platinum nanoparticles using various Monte Carlo minimization algorithms. In this study we deviate from these approaches by incorporating dynamics for the platinum atoms. Grand-canonical moves are then performed while the platinum nanoparticle is allowed to move, sampling the canonical ensemble. The main parameter of these simulations is the oxygen chemical potential of the gas reservoir which is calculated assuming ideal gas in Equation .