We report results from spin-polarized ab initio local spin-density calculat
ions for the silicon vacancy (V-Si) in 3C- and 2H-SiC in all its possible c
harge states. The calculated electronic structure for SiC reveals the prese
nce of a stable spin-aligned electron-state t(2) near the midgap. The neutr
al and doubly negative charge states of V-Si in 3C-SiC are stabilized in a
high-spin configuration with S = 1 giving rise to a ground state, which is
a many-electron orbital singlet T-3(1). For the singly negative V-Si, we fi
nd a high-spin ground-state (4)A(2) with S = 3/2. In the high-spin configur
ation,V-Si preserves the T-d symmetry. These results indicate that in neutr
al, singly, and doubly negative charge states a strong exchange coupling, w
hich prefers parallel electron spins, overcomes the Jahn-Teller energy. In
other charge states, the ground state of V-Si has a low-spin configuration.
(C) 1999 American Institute of Physics. [S0003-6951(99)04702-6].