  Extensive molecular dynamics simulations of water permeation and ion
selectivity of the single-walled carbon nanotubes with the radial deformation
are presented . The simulated results indicate that there is a close
relationship between the minor axis of deformed carbon nanotubes and the
variety, density as well as the position of functional groups. The critical
minor axis of different diameter carbon nanotubes exists, and the carbon
nanotube whose minor axis is less than the critical minor axis owns the
selectivity of chlorine and sodium ions. Meanwhile, compared with intrinsic
carbon nanotubes, the deformed nanotubes have not obviously decreased the
permeation of water. The analysis to the potential of mean force reveals that
the selectivity and permeation of ions comes from the pass potential barrier of
carbon nanotubes with various minor axises. Furthermore, our observations of
modifying with functional groups may have significance for controlling the
minor axis and improving the selectivity and permeation of ions, when it comes
to some large nanotube in real manufacture.
