  These compounds have long been known as promising thermoelectric materials.
Recently it was revealed, that they also have unconventional electronic
topology. This renewed interest to the investigation of their transport
properties. In order to improve theoretical description of thermoelectric
transport in these compounds, we take into account electron scattering beyond
commonly used constant relaxation time approximation. Using first principle
calculations, we investigate the scattering of charge carriers by phonons and
point defects. The dependence of the scattering rate on the energy correlates
with that for the total density of states. This implies that in this material
not only the intraband, but also the interband scattering is important,
especially for bands with low density of states. The Seebeck coefficient and
the electrical resistivity of CoSi and of dilute solid solutions
Co$_{1-x}$M$_x$Si (M=Fe or Ni, $x<0.1$) are calculated as a function of
temperature and the alloy composition. We show that the account of strong
energy dependence of relaxation time is important for the description of
experimentally observed rapid increase of the resistivity and qualitative
change of its temperature dependence with the substitution of cobalt for iron,
as well as for the description of the magnitude of the Seebeck coefficient, its
temperature and composition dependence.
