  In this work the effect of Carbon and Aluminium doping on the multiband MgB2
superconductor is analyzed. Using the rigid band and virtual crystal
approximations (RBA and VCA), it was found that the main effect of doping on
the band structure is band filling and a relative band-shift. If this
band-shift is eliminated with an appropriate change of scale, then the RBA
provides a good description of the band structure as function of doping. With
this procedure both the inplane electrical conductivity of the C- and Al-doped
MgB2 and the superconducting critical temperature follow the same curve. The Tc
graph approximately follows the sigma-band density of states; the differences
between these two can be explained by loss of anisotropy which plays an
important role in these systems.
