Similar to previous DFT studies of molecular dissociation on metal surfaces, we first consider HA calculations using the single lowest-energy configuration for each state (N 2 *, TS, and 2N*) and only the normal modes of the adsorbate (i.e., adsorbed N atoms) without the surface atoms. This is the most conventional usage of HA in the context of surface science, and we term this approach "single configuration HA" (SC-HA). As shown in Figure , there are large deviations in free energies between SC-HA and CFF-AIMD in the associative desorption barrier and the surface reaction energy, which are also statistically significant. Surprisingly, the two methods predict opposite trends for the temperature-dependence of Δ𝑆 ‡ (𝑇). The 𝑇Δ𝑆 ‡ (𝑇) term is nearly zero and shows a decreasing trend with temperature in SC-HA, while it is much greater than zero and increases with increasing temperature in CFF-AIMD.