  We expand the definition of our recently proposed proton conduction
mechanism, the packed-acid mechanism, which occurs under conditions of
concentrated proton donors. The original definition stated that acid-acid
interactions, which help overcome the barrier of the rate-determining step,
occur only when a hydrogen bond is formed directly between proton donors. Here,
it is shown that proton donors can interact with each other even when the
donors are separated via several H-bonds. The effect of these interactions on
proton diffusivity is confirmed by ab initio calculations.
