[lammps-users] Atoms lost in Lammps

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1

I have a simulation cell with a grain boundary and two fixed regions above and below the cell. I was trying to apply a constant force to the upper fixed region. However, I am getting an error about lost atoms.

The way I apply force is by first making the fixed region a rigid body (turning off the torque) and then using addforce command.

fix bg r rigid group 1 r torque 1 off off off

fix zfr r addforce 0.0073784 0.0 0.0 (my units are metal so force is in eV/A)

In order to fix this problem I tried the following:
1- Reducing the magnitude of the force
2- Decreasing the timestep
3- Updating neighbor list every step using neigh_modify every 1

However, none of these seem to solve my problem. I am also attaching my input file with this email. I would really appreciate if somebody can help me with this.

Thanks
-Saryu

2

There are many ways to lose atoms, due to big forces blowing
atoms away. You'll need to find out why that is happening. I suggest
viz, dumping snapshots frequently, and dumping thermo info frequently.
You can dump forces on atoms, to find out which ones are about
to be lost.

You don't need to make a rigid body to do this. You can use fix fix aveforce
and push on a wall of atoms - see examples/flow/in.flow/poiss for
an example.

Steve