From: The Cromicus Productions (
Date: Wed Nov 28 2018 - 11:41:40 CST


I have a system under an external electric field and I would like
to know if there is a flow of water. In theory I guess it shouldn't but
I tried a couple of different ways to do this with high fields (10^7 V/m)
and they all give me different results, most of them with water flow,
so I'm not sure of which one is correct. Has anyone done this before?

First I don't know if I should unwrap or not the trajectory so I tried
some codes unwrapping and some not. Then, I defined water selection
either as
      set sel [atomselect top "resname TIP3 and name OH2" frame 1]
or as
      set sel [atomselect top "resname TIP3 and name OH2" ]

and then I iterate in two different ways:
(1) $sel frame $i
       set position [measure center $sel weight mass]
(2) $sel frame $i
     $sel update

So I have wrap/unwrap, start selecion with frame 1 or not and update or not.
Some of these give me very different results, in special when I unwrap.
What do you think? What would be the correct way of analyzing whether
water is moving or not?

Thank you very much,