Suitability of ReaxFF potential for MD modelling of lithium across low and high temperatures

Modeling lithium's atomic-scale behavior is critical for its roles in plasma-facing fusion components and lithium-ion batteries, yet it remains challenging across phase regimes. This study benchmarks ReaxFF, 2NN-MEAM, and SNAP potentials from 100 to 1000 K using molecular dynamics, with ensemble and cooling protocols carefully controlled. Compared to reliable experimental data, ReaxFF diverges above 800 K, underestimating density by ~10% at 1000 K and overestimating diffusivity, yielding anomalously low-density liquid behavior. Radial distribution functions and coordination profiles further reveal possible excessive disorder above 800 K. While ReaxFF offers qualitative insight into disordered lithium, its quantitative reliability diminishes at high temperatures, requiring validation against ab initio or experimental benchmarks. These findings inform potential selections for fusion- and battery-relevant simulations, underscoring the sensitivity of glassy phase modeling to potential choices and thermal histories.