Electronic structure and properties of pure and doped epsilon-FeSi from abinitio local-density theory

Local-density calculations of the electronic structure of FeSi, FeSi1-xAlx, and Fe1-xIrxSi systems in the B20 structure are presented. Pure FeSi has a semiconducting gap of 6 mRy at 0 K. Effects of temperature (T) in terms of electronic and vibrational excitations an included. Various measurable pro perties, such as magnetic susceptibility chi(T), electronic specific heat C (T), thermoelectric power S(T), relative variations in resistivity rho(T), and peak positions in the density of states (DOS) are calculated. The feedb ack; from vibrational disorder onto the electronic structure is found to be essential for a good description of most properties, although the results for S(T) in undoped FeSi can be described up to about 150 K without conside rations of disorder. Above this T, only the filling of the gap due to disor der accompanied by exchange enhancement, can explain the large susceptiblit y. The overall good agreement with experimental data for most properties in doped and purl FeSi suggests that this system is well described by local-d ensity approximation even at large T. Doped FeSi can be described quite wel l from rigid-band shifts of the Fermi energy on the DOS of pure FeSi. Spin polarization in Ir-doped FeSi leads to a semimetallic magnetic state at low T. [S0163-1829(99)07123-3].