addforce for ReaxFF simulation

Dear all,

I face a problem to apply a specific force to a system (Al2O3) described by ReaxFF potential.
The purpose is to move a fixed region with constant shear stress (=force/area).

I write the following commands in the script:

fix 3 upper setforce 0.0 0.0 0.0
fix 4 upper aveforce 1.0 0.0 0.0

It does work well for a simple system, Cu by EAM.
However, when I apply it to Al2O3, the region where I apply force never moves.

Any one has some ideas?

Thank you.

Yunjiang Wang

What units were used for EAM and ReaxFF? Were the “1.0” changed accordingly for different unit systems?