The prominent contribution of Ag + vibrational modes to both thermal and ionic transport is made clear by comparing the vibrational frequencies of those found experimentally and from the calculated density of states (Figure ). First, the average diffuson frequency found from the spectral two-channel calculation ( $ %% = 2.3 THz) is in excellent agreement with the value estimated experimentally ( $ %% = 2.2 ± 0.2 THz, range 1.9 THz to 2.4 THz) using an analytical diffuson transport model (Supplemental Note 3). Comparatively, an average ionic transport frequency is found by using the average of the partial Ag + density of states ( _ `= 2.0 THz).