  Defect electrons (holes) play an important role in most technologically
important complex oxides; many of which possess perovskite-related structures.
In this contribution we present the first detailed characterization of
localized hole states in such materials. Our investigations employ advanced
embedded-cluster calculations which consistently include electron correlations
and defect-induced lattice relaxations. This is necessary in order to account
for the variety of possible hole-state manifestations.
