How to keep bulk material in its structure while applying electric field to push ions through ceramic material

For my LAMMPS simulation, I am trying to apply an electric field to some ions to simulate them moving through my ceramic material using Buckingham and Coulombic force-fields. The electric field is applied to the ions and the bulk of the material should remain in its structure, except for slight movements when an ion makes a hop and pushes it slightly (and temperature dependent oscillations). I have tried to fix the center of mass of the bulk material, but the result is that all atomic movement stops after a short time (a few ps at .01 V/A) when keep[ing temperature constant with nvt at 298 K. At higher electric fields this does not happen, but I would like to use smaller electric fields. I need some mechanism to keep the bulk of the material from being pushed by the ions when the electric field is applied just to the ions. Does anyone have any suggestions?

Why not apply fix efield to only your group of ions?

That is, fix EFIELD ions efield ... instead of fix EFIELD all efield ...

(bearing in mind that you’d first have to define your “ions” group with some group ions type X Y Z command first)

Can you elaborate a bit more about what kind of system this is and by what mechanism the ions are moving. From the outset it seems rather unlikely that there would be any kind of significant motion induced by a moderate electrical field on the length and time scales or classical MD simulations.

Already a easily visible response of ions solvated in liquid water to an electrical field would require very high field strengths that not possible in real experiments without turning the water into a puff of steam and some sparks.