Phonon dispersion and electron-phonon interaction for YBa 2 Cu 3 O 7 from first-principles calculations

We present a first-principles investigation of the lattice dynamics and electron-phonon coupling of the high- T c superconductor YBa 2 Cu 3 O 7 within the framework of density functional perturbation theory using a mixed-basis pseudopotential method. The calculated phonon dispersion curves are in excellent agreement with Raman, infrared and neutron data. Calculation of the Eliashberg function α 2 F leads to a small electron-phonon coupling λ = 0.27 in disagreement with earlier approximate treatments. Our calculations strongly support the view that conventional electron-phonon coupling is not an important contribution to superconductivity in high- T c materials.