Simulations of point-defect properties in graphite by a tight-binding-force model

Point-defect energetics and diffusion mechanisms in graphite are investigated using a semi-empirical tight-binding-force model. Possible diffusion processes associated with point-defect (i.e., vacancies and interstitials) and nondefect (i.e., atomic exchange) mechanisms are analyzed. It is found that self-diffusion in graphite in the direction parallel to the basal plane can be mediated by vacancies. However, since the calculated vacancy- and interstital-formation energies are nearly equal, it is argued that Frenkel pairs could exist as equilibrium defects. In this case, at high enough temperatures, self-diffusion parallel to the basal plane should occur by an interstitial mechanism because the migration energy of the interstitial is much lower.