  The LDA+DMFT (local density approximation combined with dynamical mean-field
theory) computation scheme has been used to study spectral and magnetic
properties of FeSi and Fe$_{1-x}$Co$_{x}$Si. Having compared different models
we conclude that a correlated band insulator scenario in contrast to Kondo
insulator model agrees with FeSi band structure as well as experimental data.
Coulomb correlation effects lead to band narrowing of the states near the Fermi
level with mass renormalization parameter $m^*\approx 2$ in agreement with the
results of angle-resolved photoemission spectroscopy (ARPES). Temperature
dependence of spectral functions and magnetic susceptibility calculated in DMFT
reproduces transition from nonmagnetic semiconductor to metal with local
magnetic moments observed experimentally. Cobalt doping leads to ferromagnetism
that has itinerant nature and can be successfully described by LDA+DMFT method.
