Bidirectional or unidirectional motion

Dear all,

I am doing non-equilibrium MD simulation to analyze water transport properties through CNT. My model composed of a pool region filled by SPC/E water molecules connected with a CNT. I have applied an external force on water molecules inside the pool just in Z direction (pore axis). After simulation I expect that water molecules enter the CNT from one end. But, via viz I see that water molecules enter both ends and fill the CNT length.

Could you let me know why?

Even though there are no hydrogen bonds between the graphene and the
water, there are weak attractive forces between atoms, and these can
pull them into the tube.

In LAMMPS these attractive forces are represented by the attractive
1/r^6 term in the Lennard-Jones pair-style you are probably using.

Although they are weak, I can only imagine that they would probably be
much stronger than any pressure you would be using to push the water
through the channel.

I remember there was a misconception that the hydrophobic effect would
cause water to avoid two nearby hydrophobic plates. Those 1990s
studies usually left out the dispersion force.

The important point I wanted to convey is that this is not a bug in
either LAMMPS, or the force-field you are using.


Not to dismiss your question, but if you have more followup questions
on this particular topic that aren't really LAMMPS specific, try
posting them here:
I like some of the sites. People usually reply if
you ask the question carefully (include pictures or cartoons).