Density-functional calculations of the phonon spectrum and electron-phonon coupling were presented. The E2g phonons, which involved in-plane B displacements, coupled strongly to the px,y electronic bands. The isotropic electron-phonon coupling constant was calculated to be about 0.8. Allowing for different order parameters in different bands, the superconducting λ in the clean limit was calculated to be significantly larger. The E2g phonons were strongly anharmonic, and the non-linear contribution to the coupling between the E2g modes and the px,y bands was significant.

Beyond Eliashberg Superconductivity in MgB2 - Anharmonicity, Two-Phonon Scattering and Multiple Gaps. A.Y.Liu, I.I.Mazin, J.Kortus: Physical Review Letters, 2001, 87[8], 087005 (3pp)