Ansys Chemkin allows a constant value (multiplier) for particle collision efficiency. In general, it is referred to as the van der Waals enhancement factor () and its value ranges from 1 to 3. In addition to this constant factor that simply changes the coagulation rate by a constant multiplier for all collisions, the sectional method can also use particle-size–dependent collision efficiency, which is described in Equation 19–50 .