Theoretical Evidence for Low-Spin Ground States of Early Interstitial and Late Substitutional3dTransition-Metal Ions in Silicon

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 muffintin-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.