Density-functional theory allows studies of ground-state properties of a many-electron system from first principles. Using the Green-function technique and the local density (or local spin-density) approximation, it is possible to calculate charge (ion) states, total energies, donor- and acceptor levels, and spin-densities of point defects in semiconductors. Focussing on existing open questions and controversies, the authors present results of recent theoretical studies of single substitutional and interstitial chalcogens and 3d transition-metal impurities in silicon. For the chalcogen point defects S, Se and Te they identify their positions in the silicon lattice as the substitutional site. For 3d impurities in silicon they obtain spin-multiplicities and donor and acceptor levels in good agreement with available experimental data. The early 3d interstitial and the late 3d substitutional ions are predicted to have low-spin ground states which is in conflict with the generally accepted model of Ludwig and Woodbury (LW) (1962). A large number of predictions are offered to be tested by future experimental studies.
 

Computer Physics Communications, 44 297-305, 1987.