EVOLVE is based on the free molecular or "ballistic" transport and reaction model (BTRM) developed by Timothy S. Cale

This figure is an example domain for the BTRM as used in 3D/2D simulations (see EVOLVE 3D or PLENTE for more general features)

Frequency of particle-particle collisions negligible relative to frequency of particle-wall collisions. The film evolves slowly relative to the redistribution of local fluxes. The local film growth rate is governed by heterogeneous reaction mechanisms, and depends on the local species fluxes. Species arrive at the surface from the source volume with well defined, species specific, flux distributions. System specific modifications/extensions are required; e.g., that re-emission is "cosine" for CVD systems.

• discretize integrals;
• discretize PDE using 2nd order finite difference;
• discretized equations are solved using nonlinear over-relaxation (NLORM) technique.