Pumping of Confined Water in Carbon Nanotubes by Rotation-Translation Coupling

Bidirectional single file water transport in a carbon nanotube is known to occur in ``bursts'' in short nanotubes. Here we show that in long carbon nanotubes, when the orientation of the water molecules is maintained along one direction, a net water transport along that direction can be attained due to coupling between rotational and translational motions. The rotations of the water molecules are correlated more with the translation of the neighboring water molecule with the acceptor oxygen than the neighbor with the donor hydrogen. This mechanism can be used to pump water through nanotubes.