nd - m at . s up r - co n ] 2 7 Fe b 20 01 Electron - phonon interaction in the normal and superconducting states of MgB 2

We have calculated the electronic structure in the new magnesium boron superconductor, MgB 2 , using density functional theory and the full-potential linear muffin-tin orbital (LMTO) method. We have, furthermore, calculated the complete phonon spectrum and the electron-phonon interaction using the linear-response LMTO method. We find that the B bond stretching modes with energies in the range from 800 to 900K have unusually strong coupling to electrons close to the Fermi energy at the top of the bonding quasi-two-dimensional σ-band, and a total coupling constant, λ = 0.65. We use the calculated spectral functions to evaluate various normal state and supercon-ducting properties of MgB 2 .