[lammps-users] Is "displace_atoms" command truncating small increments?

Hi,

I want to shift a group of atoms by a certain distance periodically over the course of a simulation. I am attempting to use the "displace_atoms" command, but I am encountering a problem that seems to depend on the size of the displacement. Using displace_atoms with increments > 0.1 angstrom works fine, as shown in the video at the link below.

http://www.youtube.com/watch?v=QFbH2CjCp1A

...However, increments less than 0.05 angstrom do not advance the selected group of atoms (in the pink substrate) at all. My questions are: Why doesn't the system get traction with smaller increments? Should I use a different LAMMPS command to accomplish this?

Thanks!
Nicholas J. Lee

More info: The displacements in the video are 0.1 angstrom every 10 time steps, where 1 ts = 2 fs. But the video is only a demo, it's much faster than I want. I would like to displace at rates like 0.05 angstroms per 5000 ts (or other quotients that average to > 5 m/s).

There is no truncation in displace_atoms, so something else must be
happening in your system. Have you dumped atoms before and
after the displace to verify they are not moving?

Steve