  The classical continuum theories fail to describe the ionic transport in
Angstrom channels, where conduction deviates from Ohm's law, as attributed to
dehydration/self-energy barrier and dissociation of Bjerrum ion-pairs in
previous work. Here we found that the cations are strongly bound to the surface
charge that blockade the ionic transport in a single-file water channel,
causing nonlinear current-voltage responses. The presence of free ions
significantly increased the probability of bound ions being released, resulting
in an ionic current. We found that ionic conduction gradually becomes Ohmic as
surface charge density increases, but the conduction amplitude decreased due to
increased friction from bound ions. We rationalized the ionic transport by 1D
Kramers' escape theory framework, which well described nonlinear ionic current,
and the impact of surface charge density on turning to Ohmic system. Our
results possibly provide an alternative view of ionic blockade in Angstrom
channels.
