[lammps-users] Surface distorting during simulation

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1

I am trying to run a simulation looking at the absorption of surfactant molecules within an oil solvent, onto an alumina surface.

I have set up the my surface, surfactants and oils and defined all the required force field parameters etc.

However, when I run my simulation I am getting large fluctuations and distortions of the surface. For instance under an NVT, the surface start flat, but ends up warped and at about 45deg angle. (This does not happen when doing an NVT on the lone surface)
A similar thing happens under NPT.

I am looking to do an anisotropic NPT with my simulation cell changing in the z direction only, so I get my fluid to required density/pressure. I do not want any changes or rescaling of my surface structure.

Is there anything I can do to stop my surface warping and distorting. Can I anchor certain atoms in place to stop it moving or is there a better way to deal with this. What is the best fix npt options to use in this case, for this type of system.

Thanks.
Michael Doig

2

I am trying to run a simulation looking at the absorption of surfactant
molecules within an oil solvent, onto an alumina surface.

[...]

Is there anything I can do to stop my surface warping and distorting.
Can I anchor certain atoms in place to stop it moving or is there a
better way to deal with this. What is the best fix npt options to use in
this case, for this type of system.

this sounds more like there are issues with your force field parameters,
particularly the interaction of your surface and whatever you put on it.

i don't think this has anything to do with the integrator, but it is
impossible to tell from just a description.

cheers,
   axel.