  The electronic structure of diluted (Ga,Mn)As magnetic semiconductors in the
presence of As-antisites and magnetic disorder is studied within the framework
of the local spin density approximation. Both the chemical and magnetic
disorders are treated using the coherent potential approximation. A ground
state with partial disorder in the local moments and with a reduced total
magnetic moment appears in the presence of As-antisites. We first estimate the
Curie temperature T_c from total energy differences between the ferromagnetic
and the paramagnetic state by identifying these with the corresponding energy
difference in a classical Heisenberg model. A more systematic approach within
the framework of the mean-field approximation to estimate T_c consists in an
evaluation of the effective exchange fields acting on the magnetic moment at a
given site. The presence of As-antisites strongly reduces the Curie
temperature. The results indicate that the effect of impurities on the
electronic structure cannot be neglected and influences the Curie temperature
non-negligibly. A comparison of the calculated Curie temperatures to existing
experimental data indicates an increase of the donor concentration with the
increase of the Mn-content.
