Another view of electron-phonon coupling revealing peak-like structures in q-space

We derived the electron-phonon matrix elements from extended degenerate perturbation theory. This leads to a simple understanding of the electron-phonon interactions in terms of a dynamic pseudo-Jahn-Teller effect. Based on the linear response theory we have calculated such electron-phonon matrix elements for Ca and Hg. A new quantity NDOS(lambda) is proposed to analyse the population of phonon modes with respect to the electron-phonon coupling. Our results indicate strong q-dependence of the electron-phonon coupling constants in both cases, Ca and Hg; with only Hg being expected to become superconducting. (C) 2001 Elsevier Science Ltd. All rights reserved.