To show that no reaction can occur. You start with two atoms with an energy less than zero, and find that the two atoms can never dissociate.
The A-B potential is assumed to be a morse potential with a well depth of 10 kcal/mole and a range parameter of 1.5 angstroms. When I teach my course, I use this example to show that if you start with a stable molecule, the molecule remains stable unless the molecule collides with something and accumulates energy.
For further information about applications of this program please look in Chapter 9 of R. I. Masel, Principles of Adsorption and Reaction on Solid Surfaces, Wiley 1996 or Chapter 8 of R. I. Masel, Kinetics and Catalysis, Wiley 2000