Properties of KCo${}_2$As${}_2$ and Alloys with Fe and Ru: Density Functional Calculations

Electronic structure calculations are presented for KCo${}_2$As${}_2$ and alloys with KFe${}_2$As${}_2$ and KRu${}_2$As${}_2$. These materials show electronic structures characteristic of coherent alloys, with a similar Fermi surface structure to that of the Fe-based superconductors, when the $d$ electron count is near six per transition metal. However, they are less magnetic than the corresponding Fe compounds. These results are discussed in relation to superconductivity.