  It has long been accepted that the multiple-ion single-file transport model
is appropriate for many kinds of ion channels. However, most of the purely
theoretical works in this field did not capture all of the important features
of the realistic systems. Nowadays, large-scale atomic-level simulations are
more feasible. Discrepancy between theories, simulations and experiments are
getting obvious, enabling people to carefully examine the missing parts of the
theoretical models and methods. In this work, it is attempted to find out the
essential features that such kind of models should possess, in order that the
physical properties of an ion channel be adequately reflected.
