Electronic structure of the pyrochlore metals (formula presented) and (formula presented)

First-principles density-functional calculations within the local spin-density approximation and the generalized gradient approximation are reported for pyrochlore (formula presented) and (formula presented) The transition-metal (formula presented) manifolds are found to be well separated in energy from the O (formula presented) bands and from the higher-lying (formula presented) and Cd derived bands. The active electronic structure in the (formula presented) manifold near the Fermi energy (formula presented) is found to be significantly modified by spin-orbit interactions, which we include. Both materials show semimetallic band structures, in which the (formula presented) lies in an pseudogap. The band structure of (formula presented) near (formula presented) is dominated by very heavy-hole and electron bands, though at (formula presented) the electron sections are lighter. (formula presented) has heavy-hole bands but moderate mass electron states. The results are discussed in terms of measured transport and thermodynamic properties of these compounds as well as the very different ground states of these two materials.