PHONON DISPERSION CURVES

The calculated phonon dispersion curves along the high-symmetry directions of the Brillouin-zone (see inset to Fig.1) are shown in Fig.2 (click here to see it above).

All the modes are found to be quite dispersive as expected for the small size of the unit cell, but divide nearly completely into acoustic (below 40 meV) and optical (50-100 meV) bands, with the only exception being along the A-L direction. All the optical modes are weakly dispersive along the G-A direction, reflecting the layered nature of the MgB₂ crystal structure.

At the zone center (G) , the symmetries of the modes are also indicated. The modes indicated by the red-line are found to be very anharmonic and dominate the electron-phonon coupling.