ab-initio total energy calculation and the hyperfine interactions of iron-acceptor pairs in silicon

We present ab-initio total energy calculations for trigonal and orthorhombic pairs of iron with B, Al, Ga and In accepters which have been carried out in the Local Spin Density Approximation to the Density Functional Theory. We have used a Green's function technique and a Linear Muffin-Tin Orbitals Method within the Atomic Spheres Approximation. We have determined the pair binding energies and electron removal energies for the defects considered. Except for the orthorhombic (FeGa)(+) we have found high-spin ground states in all charge states +, 0 and -. For (FeGa)(+) we find a S = 1 ground state. We also present our calculated hyperfine interactions for the neutral pairs of trigonal and orthorhombic symmetry. Taking into account the combined influence of the spin-orbit interaction and of the crystal fields induced by the shallow accepters we have been able to determine the ground states studied in magnetic resonance experiments. All calculated hyperfine data show reasonable agreement with the experimental data. This shows that it is possible to estimate the orbital reduction factors to a large extend with the help of the self-consistently calculated spin densities of the LSDA-DFT.