Optical near-zone-center phonons and their interaction with electrons in YBa2Cu3O7: Results of the local-density approximation

Abstract

Ab initio frozen-phonon calculations were performed for ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ for the five ${\mathit{A}}_{\mathit{g}}$ Raman-active and for two ${\mathit{B}}_{1\mathit{u}}$ infrared-active optical q=0 modes, with use of the local-density approximation and the full-potential linear-muffin-tin-orbital method. The full ${\mathit{A}}_{\mathit{g}}$ dynamical matrix was calculated using 98 k points in the 1/8 Brillouin zone. The theoretical and experimental equilibrium structures and phonon frequencies ${\mathrm{\omega }}_{\nu }$ agree well. Phonon linewidths ${\gamma }_{\nu \mathbf{q}}$, due to electronic intraband transitions in the normal state, and electron-phonon coupling constants ${\lambda }_{\nu \mathbf{q}}$==${\gamma }_{\nu \mathbf{q}}$/[πN(0)${\mathrm{\omega }}_{\nu }^2$] were calculated for the ${\mathit{A}}_{\mathit{g}}$ modes and small, transverse q. We estimate that λ≊1 for the sum over all modes. The phonon shifts and broadenings observed for T<${\mathit{T}}_{\mathit{c}}$ by Raman scattering are well accounted for by conventional strong-coupling theory and our calculated electron-phonon coupling.