OPTICAL NEAR-ZONE-CENTER PHONONS AND THEIR INTERACTION WITH ELECTRONS IN YBA2CU3O7 - RESULTS OF THE LOCAL-DENSITY APPROXIMATION

Ab initio frozen-phonon calculations were performed for YBa2Cu3O7 for the five Ag Raman-active and for two B1u infrared-active optical q=0 modes, with use of the local-density approximation and the full-potential linear-muffin-tin- orbital method. The full Ag dynamical matrix was calculated using 98 k points in the 1/8 Brillouin zone. The theoretical and experimental equilibrium structures and phonon frequencies agree well. Phonon linewidths q, due to electronic intraband transitions in the normal state, and electron-phonon coupling constants q==q/[N(0) 2] were calculated for the Ag modes and small, transverse q. We estimate that 1 for the sum over all modes. The phonon shifts and broadenings observed for T<Tc by Raman scattering are well accounted for by conventional strong-coupling theory and our calculated electron-phonon coupling. © 1990 The American Physical Society.