The ratio between the self-and charge-diffusion coefficients is the Haven ratio, H R = D * /D σ , which provides a measure of the degree to which the motions of different Li + ions are spatially correlated . If the diffusion of mobile ions is completely uncorrelated then D σ = D * and H R = 1. The calculated Haven ratio is shown as a function of temperature in Figure ). It is likely that the Haven ratio increases with temperature and that diffusion becomes weakly correlated with the motion of neighbouring ions at higher temperatures due to the increased defect concentration. Decreasing dynamic correlation between mobile ions has been observed across the superionic transition of AgCrSe 2 and fluorites . Nevertheless, as our data analysis is very noisy, it is not possible to assert such conclusions from Figure only. Simulations with longer timescales are likely to be required in order to converge values for the Haven ratio at all temperatures. The timesteps in the simulation were sub-sampled to allow for easier post-processing. To represent the diffusive dynamics observed in the simulations, the sub-sampling is adjusted according to the observed rate of diffusion. At low temperatures, the simulation is not truncated, but the sub-sampling is coarse. At high temperatures, the simulation is truncated, but the sub-sampling is fine. At temperatures lower than or equal to 300 K, the vacancy fraction remains null for all sub-sampled timesteps. Figure : Average phonon linewidth against Mean Square Displacements (MSD). The linewidth becomes larger than a critical linewidth Γ c at any temperature, regardless of the diffusion regime (normal or superionic), provided the MSD are high enough. The highlighted grey area show that when MSD are approximately constant, the linewidth values also remain approximately constant for all temperatures. The computational method used to compute anharmonic phonon properties is not reliable when nonnegligible diffusion occurs.