First-principles total energy calculations were made, of trigonal and orthorhombic pairings of Fe with B, Al, Ga or In acceptors, by using the local spin density approximation of density functional theory. A Green’s function technique, and a linear muffin-tin orbitals method, were used within the atomic spheres approximation. The pair binding energies and electron removal energies for the defects were determined. Except for orthorhombic (FeGa)+, high-spin ground states were found for charge states of +, 0 and -. An S = 1 ground state was found in the case of (FeGa)+. Calculated hyperfine interactions were also performed for neutral pairs with trigonal and orthorhombic symmetry. By taking account of the combined effects of spin-orbit interactions and of the crystal fields which were produced by the shallow acceptors, it was possible to determine the ground states which were studied in magnetic resonance experiments. All of the calculated hyperfine data exhibited a reasonable agreement with experimental data. This showed that it was largely possible to estimate the orbital reduction factors with the aid of self-consistently calculated spin densities.

H.Weihrich, H.Overhof: Materials Science Forum, 1995, 196-201, 1327-32