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

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