First-principles energy calculations, in the local spin density approximation of density functional theory, were made of interstitial Fe. A Green’s function technique was applied to the linear muffin-tin orbitals method within the atomic spheres approximation. Unfortunately, the use of the latter approximation did not permit lattice relaxations to be taken into account. The results of a detailed examination of the induced density of states led to a covalent model for the electronic structure of interstitial Fe. Hyperfine interactions were calculated for the interaction with 57Fe (+ and 0 charge states) and for the interaction with several shells of 29Si atoms. The results revealed that the marked smallness of the orbital reduction factor which was measured in electron paramagnetic resonance could not be explained by covalent effects alone, but strongly indicated the occurrence of a dynamic Jahn-Teller effect.

H.Weihrich, H.Overhof: Materials Science Forum, 1995, 196-201, 677-82