[lammps-users] A general question about 'freezing' (set force 0.0) of surface atoms

Dear Lammps users,

I have a general question and I am looking for some insights from experienced
I am trying to simulate a liquid on a surface. I am interested to know the
structural ordering, diffusion of the liquid molecules due to the presence of
the surface.

Is it OK to keep all surface atoms fixed (rigid surface) ? ( I see some papers
where surface atoms are kept fixed in such simulation).
What information will I miss if the atoms are fixed ?

Thanks for any comments


It depends strongly on specifically what physical question you’re investigating, what the interactions between surface and liquid are, what the temperature is, etc. You should think about these things first, then read relevant background material, etc. As many will point out to you here, the physical consequences of freezing surface atoms don’t have much to do with LAMMPS per se.


One simple effect of freezing the surface is less diffusion
of surface atoms. An adatom is less likely to hop if the
atoms underneath it can't relax to lower the hopping barrier.