Displaced charge and formation energies of point defects in metals

Two approaches to the calculation of point defect properties have often been adopted, with rather different aims: (i) the pair potential approach and (ii) the electron theory, characterized by the charge displaced by the defect. (i) is only quantitatively applicable to vacancies and interstitials when a 'rigid ion' or 'pseudoatom' model is valid. Alternative approaches based on Wannier functions and, for simple metals, on pseudopotentials, are discussed. A tight binding model for formation energies in transition metals is referred to and finally a theory in which relaxation effects can be approximately incorporated in a calculation of the charge displaced by a defect is outlined.