  The electronic structures of Mn-doped zincblende GaAs and wurtzite GaN are
calculated using both standard local-density functional theory (LSDA), and a
novel pseudopotential self-interaction-corrected approach (pseudo-SIC), able to
account for the effects of strong correlation. We find that, as expected, the
self-interaction is not strong in (Ga,Mn)As, because the Fermi energy is
crossed by weakly correlated As p - Mn d hybridized bands and the Mn 3d
character is distributed through the whole valence band manifold. This result
validates the extensive literature of LSDA studies on (Ga,Mn)As, including the
conclusion that the ferromagnetism is hole-mediated. In contrast, the LSDA
gives a qualitatively incorrect band structure for (Ga,Mn)N, which is
characterized by localized Mn 3d bands with very strong self-interaction. Our
pseudo-SIC calculations show a highly confined hole just above the Fermi energy
in the majority band manifold. Such a band arrangement is consistent with
(although by no means conclusive evidence for) a recent suggestion that
formation of Zhang-Rice magnetic polarons is responsible for hole-mediated
ferromagnetism in (Ga,Mn)N.
