Extended Hückel theory calculations were carried out on several two-dimensional models of graphite in order to examine the usefulness of this technique in calculating atom migration energies in solids. The calculations yield an activation energy of 2.3eV for vacancy migration and an activation energy of 25.3eV to form a Frenkel pair 3.8Å apart, which could be compared with the experimental values of 3.15eV for vacancy migration and 25eV for the displacement threshold.

Extended Hückel Theory Calculation of Atom Migration Energies in Two-Dimensional Graphite. Moore., E.B., Carlson, C.M.: Solid State Communications, 1966, 4[1], 47-9