Our calculated self-diffusion coefficients over the complete range of simulation temperatures exhibit non-Arrhenius behaviour (Figure ); the gradient d ln D * /dT is smaller at high temperature, corresponding to a lower activation energy, than at low temperature. By subdividing our self-diffusion coefficient data into lowtemperature "normal" (T < 675 K) and high-temperature "superionic" (T > 575 K) subsets, we find two regimes with distinct Arrhenius behaviours. Distinct Arrhenius behaviours in the normal and superionic regimes have been observed in other superionic conductors including fluorites and AgCrSe 2 . From our D * xyz data, we assign activation energies of E a,n = 0.4097( and the ratio D * xy /D * z decreases with temperature, which agrees with the experimentally observed decrease in conductivity anisotropy reported for Li 3 N single crystals . The change in self-diffusion activation energy across the superionic transition temperature suggests a corresponding change in how Li + ions migrate: either the ease with which individual ions migrate, or a change in the fraction of Li + ions that participate in diffusion in a given time window.