Ground-state total energies and spins have been calculated for all interstitial and substitutional 3d ions in crystalline Si by use of spin-unrestricted density-functional theory plus the linear muffin-tin-orbital Green's-function method. The calculated deep donor and acceptor levels reproduce for the first time all experimentally observed transitions. The early 3d interstitial ions and the late 3d substitutional ions are calculated to have low spin. This is in conflict with the generally accepted model due to Ludwig and Woodbury (1962).
 

Physical Review Letters, 55 1498-501, 1985.