# Catalysis:Intermolecular Potential

The catalysis module uses an atomic model (O and C atoms, as well as surface atoms, are each represented explicitly). All atoms interacts via a square-well intermolecular potential. The functional form of the square well potential is shown below:

{\displaystyle u(r)={\begin{cases}{\begin{aligned}\infty {\text{ if r}}\leq \sigma \\-\epsilon {\text{ if r}}<\lambda \sigma \\0{\text{ if r}}\geq \lambda \sigma \end{aligned}}\end{cases}}}        (Equation 8)

where ${\displaystyle \sigma }$ is the collision diameter, ${\displaystyle \epsilon }$ is the well depth (minimum potential energy), and ${\displaystyle \lambda }$ is the reduced well width.

Graphically, the SW potential can be representated as:

All atoms interacting with the surface must have 3 surface sites (atoms) to react/adsorb, or to become stable on the catalyst surface. Diatomic species (CO and O2) require 2 sites to adsorb. The triatomic product CO2, once formed, does not dissociate (thermodynamically stable).

The atoms are propagated through time and space using the discontinuous molecular dynamic (DMD) method, in conjunction with the square well potential mentioned above.