The properties of the vacancy were deduced by using first-principles calculations. The ground-state structure was associated with a formation energy of 7.4eV, and arose from a combination of symmetrical relaxation and symmetry-breaking Jahn-Teller distortion of one of 3 degenerate symmetry-related structures. The distortion resulted in a weak reconstructed bond, and small out-of-plane atomic displacements. Dynamic switching between degenerate structures was activated by a barrier of 0.1eV, and scanning tunneling microscopy observations were interpreted in terms of thermal averaging between structures. The calculated migration energy (1.7eV) was lower than the experimental value, and it was suggested that the discrepancy was due to a trapping, during vacancy transport, that depended upon concentration.

Structure and Energetics of the Vacancy in Graphite. A.A.El-Barbary, R.H.Telling, C.P.Ewels, M.I.Heggie, P.R.Briddon: Physical Review B, 2003, 68[14], 144107