Thanks for your reply. I am still having difficulty giving the bombardment atom a velocity. There are two molecule blocks, the first one runs fine, I use all the parameters given in the tutorial. The second molecule block is tricky. For one, the version I'm using doesn't have the "velocity configuration" option under "initial velocity," there's only the "Maxwell-Boltzmann" option.
I also need to understand how to make the modifications to the script in the editor similar to that shown in the tutorial.