· Atomic models of the diffusion process must establish how atoms migrate in a crystal structure, determine the energy associated with the process and how it is transferred to the atoms, and relate this to the macroscopic diffusion coefficient and diffusion energy.
· For an interstitial atom in a simple cubic lattice, the body center sites (1, 3) have the lowest Gibbs free energy. The face centered site (3) has a higher Gibbs free energy, the repulsive interaction with the nearest atoms being largest there.

· The Gibbs function of a migrating interstitial varies with position as shown. This behavior is periodic with the interstitial site periodicity.