Best practice and validation for interatomic potentials of molecular dynamics modeling of ice in planetary science

Reliable molecular dynamics (MD) simulations of water ice in planetary environments require interatomic potentials (IP) that reproduce both structural and mechanical behavior over wide thermodynamic conditions. This work benchmarks two reactive force fields (ReaxFF), against the rigid TIP4P/Ice model and available experimental data for crystalline and amorphous ice at extreme conditions. Elastic modulus, density, oxygen self-diffusion, and isothermal compressibility are evaluated across temperatures from 25 to 264 K and under varying formation histories. Stress–strain analyses show that crystalline ice exhibits brittle behavior, while amorphous ice displays enhanced ductility and strong dependence on thermal history. The ReaxFF IPs reproduce elastic moduli and densities in close agreement with TIP4P/Ice and experiment but have variable success in reproducing diffusive and compressibility trends. Additionally, computational tests demonstrate that ReaxFF is more CPU demanding than rigid models. Here we validate the use of a hybrid workflow in which structural equilibration is performed with TIP4P/Ice and reactive dynamics are applied only where needed. These results establish quantitative guidelines for selecting and validating IPs for simulations of ice in planetary and space environments and provide a foundation for future studies of reactive processes in icy systems.