  We present first-principles electronic structure calculations of Mn doped
III-V semiconductors based on the local spin-density approximation (LSDA) as
well as the self-interaction corrected local spin density method (SIC-LSD). We
find that it is crucial to use a self-interaction free approach to properly
describe the electronic ground state. The SIC-LSD calculations predict the
proper electronic ground state configuration for Mn in GaAs, GaP, and GaN.
Excellent quantitative agreement with experiment is found for magnetic moment
and p-d exchange in (GaMn)As. These results allow us to validate commonly used
models for magnetic semiconductors. Furthermore, we discuss the delicate
problem of extracting binding energies of localized levels from density
functional theory calculations. We propose three approaches to take into
account final state effects to estimate the binding energies of the Mn-d levels
in GaAs. We find good agreement between computed values and estimates from
photoemisison experiments.
