Experimenting with VdW parameters

Now that you know how to change the VdW parameter, here are a few more experiments that you can do.

• When you made the pore larger by reducing the carbons' radii, you decreased the surface of the favorable VdW interactions between the permeating water molecules and the nanotube. Instead of being surrounded by carbon, the waters are now only attracted to one side, and therefore the water-nanotube interaction is much smaller. Can you change the carbon's VdW maximum binding energy (epsilon in the parameter file) so that the water file remains stable inside the pore (as opposed to leaving the pore as before), while still keeping a small carbon VdW radius parameter of 0.5? Make sure that epsilon is always negative or else the simulation won't run.

• Revert your changes by recopying the original parameter file. What happens if you slightly increase the carbons' VdW radius parameter so as to increase the contact area with water? How can you observe this increased interaction in your water file? Can you find the optimal epsilon that will maximize the number of water molecules in the pore?