Unraveling the Jahn-Teller effect in Mn-doped GaN using the Heyd-Scuseria-Ernzerhof hybrid functional

We present an ab-initio study of the Mn substitution for Ga in GaN using the Heyd-Scuseria-Ernzerhof hybrid functional. Contrary to semilocal functionals, the majority Mn t₂ manifold splits into an occupied doublet and an unoccupied singlet well above the Fermi level resulting in an insulating ground state, which is further stabilized by a sizeable Jahn-Teller distortion. The predictions are confirmed using $GW$ calculations and are in agreement with experiment. A transition from a localized to a delocalized Mn hole state is predicted from GaN to GaAs.