When atoms land on a surface, there are two possibilities. First, they would diffuse on the surface and find other atoms to make a cluster, which will be discussed below. Second, they could come off of the surface or so-called desorption process. The desorption is described exactly as in the absorption process, with the exception of a different activation energy barrier.
For example, if all positions on the surface of the crystal are energy equivalent, the rate of growth can be calculated from Turnbull formula:
where  is the rate of growth, ∆G = E – E, A, A are frequencies to go in or out of crystal for any given molecule on the surface, h is the height of the molecule in the growth direction and C the concentration of the molecules in direct distance from the surface.