  The electronic structures of Ba(Fe,Ru)$_2$As$_2$ and Sr(Fe,Ir)$_2$As$_2$ are
investigated using density functional calculations. We find that these systems
behave as coherent alloys from the electronic structure point of view. In
particular, the isoelectronic substitution of Fe by Ru does not provide doping,
but rather suppresses the spin density wave characteristic of the pure Fe
compound by a reduction in the Stoner enhancement and an increase in the band
width due hybridization involving Ru. The electronic structure near the Fermi
level otherwise remains quite similar to that of BaFe$_{2}$As$_{2}$. The
behavior of the Ir alloy is similar, except that in this case there is
additional electron doping.
