  We report a multiscale modeling study for charged cylindrical nanopores using
three modeling levels that include (1) an all-atom explicit-water model studied
with molecular dynamics (MD), and reduced models with implicit water containing
(2) hard-sphere ions studied with the Local Equilibrium Monte Carlo simulation
method (computing ionic correlations accurately), and (3) point ions studied
with Poisson-Nernst-Planck (PNP) theory (mean-field approximation). We show
that reduced models are able to reproduce device functions (rectification and
selectivity) for a wide variety of charge patterns; that is, reduced models are
useful in understanding the mesoscale physics of the device (i.e., how the
current is produced). We also analyze the relationship of the reduced
implicit-water models with the explicit-water model and show that diffusion
coefficients in the reduced models can be used as adjustable parameters with
which the results of the explicit- and implicit-water models can be related. We
find that the values of the diffusion coefficients are sensitive to the net
charge of the pore, but are relatively transferable to different voltages and
charge patterns with the same total charge.
