Electron–Phonon Interaction in Simple Metals: Beyond the Diffraction Model

The exact solution to the self-consistent field screening problem presented in a previous paper (Moore et al.), reduces in the weak pseudopotential limit to the diffraction model for the electron–phonon matrix element, and in particular to Animalu's expression for the screening of a nonlocal pseudopotential. Systematic corrections to the diffraction model, including local field effects, are presented for a pseudopotential of moderate strength; these corrections are particularly simple when the pseudopotential is local. Local pseudopotential calculations of the anisotropic electron–phonon form factors indicate that corrections to the diffraction model are small in sodium but substantial in lithium.