Phonon‐induced self‐energy and mass enhancement of electrons in metals

The phonon‐induced energy correction of electrons in metals and the resulting change of the effective mass are formulated by means of localized functions (i.e. generalized Wan‐nier functions). This formulation makes it possible to take into account, in a simple way, the experimentally observed anisotropies of the Fermi surface and the Fermi velocity. The periodicity of reciprocal space is preserved, thus all “Umklapp” processes are included. As an application of this formulation the κ‐dependent mass enhancement parameter λ(κ) is evaluated for Cu. λ(κ) varies from 0.086 (in 〈100〉 direction) up to 0.185 (at the neck of the Fermi surface); the average is found to be 0.15.