Electronic structure and superconductivity in metal hexaborides

The electronic structure and the phonon modes of the superconducting cluster compounds LaB6 and YB6 are evaluated. They are used to calculate the Eliashberg function of both compounds within the rigid-muffin-tin approximation for electron-phonon coupling. The individual contributions from the different phonon branches are discussed. It turns out that nonlocal corrections to the electron-phonon coupling are essential for those modes where the B6 octahedras move as a whole. Omission of these corrections leads to a large overestimate of lambda and T/sub c/