quartz etching

Hello everyone;

I am a new with Lammps. I want try to simulate argon bombardment onto a amorphous silica. I have obtained the structure that I desired,however I have some question on how to model the bombardment.

How do i set up the initial position? I already have the amorphous silica but how should I place the argon atoms on top of the amorphous silica?


The fix deposit command can shoot atoms into a substrate
with a defined velocity.