Nonspherical rigid-muffin-tin calculations of electron-phonon coupling in high-Tcperovskites

The Hopfield factor (electronic part of the electron-phonon coupling constant) is calculated in the rigid-muffin-tin approximation (RMTA) for several perovskite high-${\mathit{T}}_{\mathit{c}}$ superconductors. Calculations were performed in the conventional ‘‘spherical’’ approximation and take into account the proper local symmetry. It is shown that the layered perovskite crystal symmetry generally favors strong electron-phonon interaction on the copper sites. We also estimate some non-RMTA effects.