Understanding the negative vacancy in silicon without configuration interaction theory

We have calculated the electronic structure of the lattice vacancy in silicon in the negative charge state V- using the self-consistent charge density-functional theory based tight-binding scheme for the computation of large supercells containing up to 512 atoms in combination with the linear muffin-tin orbitals method in the atomic-spheres approximation. Many-body effects are treated in the local spin density approximation of the density functional theory (LSDA-DFT). We find the ground state of the V- to be the low-spin B-2(1) state of the group C-2v, which is lower in energy by 0.09 eV than the (4)A(2) high-spin state of the group T-d. We have also calculated the hyperfine interactions with 18 shells containing 46 Si-29 ligand atoms. We find the largest HF interactions in the (1 (1) over bar0) plane in agreement with experimental data. The HF interactions with nuclei in the (110) plane, which are about two orders of magnitude smaller than those with nuclei in the (1 (1) over bar0) plane, also agree with the experimental data. We conclude that the LSDA-DFT describes the magnetization density of the V- well. It is therefore not necessary to include configuration interactions as has been proposed by M. Lannoo [Phys. Rev. B 28, 2403 (1983)].