  Based on first-principle FLAPW-GGA calculations, we have investigated the
systematic trends in structural and electronic properties of a newly discovered
group of ThCr2Si2-like arsenides: SrRu2As2, BaRu2As2, SrRh2As2 and BaRh2As2.
Our results show that the replacement of an alkaline earth metal (Sr - Ba) and
4d metal (Ru - Rh) leads to various types of anisotropic deformations of the
crystal structure caused by strong anisotropy of inter-atomic bonds.
  The band structure, density of states and Fermi surfaces have been evaluated
and discussed. Appreciable changes in the near-Fermi bands and the Fermi
surface topology found as going from (Sr,Ba)Ru2As2 to (Sr,Ba)Rh2As2 reflect the
growth of the 3D-like type of dispersion for these systems, which is
accompanied by an increase in the near-Fermi density of states. The
inter-atomic bonding in (Sr,Ba)(Ru,Rh)2As2 phases adopts a complex anisotropic
character, where the bonding in [(Ru,Rh)2As2] blocks is of a mixed
metallic-ionic-covalent type whereas between adjacent [(Ru,Rh)2As2] blocks and
(Sr,Ba) atomic sheets, ionic interactions emerge; thus these systems may be
classified as ionic metals.
