Before revision: 3), where z = 2 for 1D diffusion as would be the case for in-channel diffusion, z = 4 as in a square lattice , and z = 6 as in a hexagonal lattice.
After revision: 3), where z = 2 for 1D diffusion as would be the case for in-channel diffusion, z = 4 for 2D diffusion , and z = 6 as in a hexagonal lattice.