[gmx-users] Re: Water spreading on graphene!

[Dr. Vitaly Chaban]

Yes, the water droplet should remain a droplet on graphene.

Since you have a droplet, I assume you have much vacuum in the system. I
would not use PME for such system, but would rather "compensate" it by
using larger cutoffs.

If you need a simple advice, it is -- enlarge the box to avoid any
interactions, which you would not have had in real experiment.

I also expect a specific behavior, if your droplet is very small.

Maybe, I would simulate this system without PBC at all.


Dr. Vitaly Chaban







> I have a graphene like surface (carbons on a hexagonal lattice with zero
> partial charges and some LJ parameters) with a drop of water placed on it.
> In principle, this is a hydrophobic surface and the drop should remain a
> droplet on it. However, surprisingly I am seeing that the drop is spreading
> within a 1 ns of the simulation. In the past I have done some similar
> simulations (with a different structure but basically zero partial charge
> surface and LJ) on which the drop remains a drop.
>
> Does any body have any ideas of what I may be doing wrong? Pasted below is
> my mdp and top file. Briefly, I am doing NVT simulation, PME for
> electrostatics, TIP3P water model, the surface is frozen and intra-surface
> interactions are excluded, the cut-off distances are 1 nm, velocity rescale
> thermostat (I tried both with the entire system coupled to the same
> thermostat and with sheet and water being coupled to different
> thermostats).
> Any suggestions are welcome.
>
> My analysis suggests this comes from the long range electrostatics because
> we have tested the same thing in LAMMPS. When we turn off PPPM and use
> cut-off based Coulomb (~5 nm) in LAMMPS (yes now we have changed the
> software) we don't see the drop spreading.
>
> I have done so many simulations and to have this problem stumps me!! Thanks
> for being helpful always.
>