A series of calculations on MgB2 and related iso-electronic systems indicated that the layer of Mg2+ ions lowered the non-bonding B π(p(z)) bands relative to the bonding σ (spxpy) bands compared to graphite, causing σ-->π charge transfer and σ-band doping of 0.13 holes/cell. Because of their 2-dimensionality, the σ-bands contributed strongly to the Fermi level density of states. Calculated deformation potentials of γ point phonons identified the B bond stretching modes as dominating the electron-phonon coupling. Superconductivity driven by σ band holes was consistent with the report of destruction of superconductivity by doping with Al.

Superconductivity of MgB2. J.M.An, W.E.Pickett: Physical Review Letters, 2001, 86[19], 4366-9