DFT calculations are used to explain states in TPD spectra by relating the differential adsorption energies for different configurations to the desorption features. A plot of the number of molecules versus these temperatures strongly resembles the TPD spectrum. The calculations were also used to obtain pairwise additive potentials. These potentials were used in a dynamic Monte Carlo model to simulate the TPD spectrum. The spectra obtained from both approaches are in good agreement, validating the approximation that lateral interactions can be added on a pairwise basis.