PHONONS AND SUPERCONDUCTIVITY IN YBA2CU3O7

We report the results of a calculation of the electron-phonon interaction in YBa2Cu3O7 based on the nonorthogonal tight-binding approach to lattice dynamics. A self-consistent local-density electronic-structure calculation was combined with a shell-model description of the phonon spectrum. The resulting interaction matrix was used to calculate the superconducting transition temperature from a solution of the Eliashberg equations in which the full k dependence was retained. The transition temperature was found to be about 90 K, quite close to experiment. The oxygen isotope effect was investigated. We also calculated the k-dependent gap function at T=0. The gap shows significant variation between different sheets of the Fermi surface as well as dependence on k on the individual sheets, but is nodeless. The quantity 2DELTA/k(B)T(c) varies from 6.0 to 2.5 on the Fermi surface.