Benchmarking Classical Force Field for Na ⁺ Transport in Na ₃ Zr ₂ Si ₂ PO ₁₂ Solid Electrolytes: A First-Principles Study

We present a critical assessment of the force-field model of NASICON solid electrolytes, benchmarking it against ab initio molecular dynamics (AIMD) and nudged elastic band (NEB) calculations. While the classical molecular dynamics (CMD) employing the force field slightly overestimates the rigidity of the Na3Zr2Si2PO12 polyhedral skeleton, it yields remarkable agreement with AIMD in predicting Na+ migration channels and overall mobility. Our results validate the accuracy of CMD-derived predictions on the pivotal role of Si/P ordering in governing ion transport. Furthermore, AIMD trajectories reveal that ion transport involves a cooperative mechanism between Na+ and the polyhedral skeleton, as evidenced by the significant drop in ion mobility upon freezing the framework dynamics, consistent with the earlier CMD predictions. These findings suggest that the model offers a cost-efficient platform for exploring aliovalent substitutions of chemically simple dopants, in search of highly conducting compositions within the NASICON-family.