  Electronic structures of orthorhombic ternary nickel silicides:
superconducting Lu2Ni3Si5 and its non-superconducting counterpart, Y2Ni3Si5,
have been calculated employing the fully-relativistic and full-potential
local-orbital method within the density functional theory. Our investigations
were focused particularly on the band structures and Fermi surfaces (FSs),
being very similar for both ternaries. It appears that their FSs exist in four
bands and contain electronlike and holelike three-dimensional sheets and small
pockets, which suggests a presence of two- or even multi-band superconductivity
(SC) in Lu2Ni3Si5. The main difference between both systems is that only in
Lu2Ni3Si5 small electron FS pockets occur around the Gamma point. It allows for
arising BCS-like SC in this compound, as was deduced from previous
heat-capacity measurements, while no sign of SC has been detected (at least
down to 2 K) in Y2Ni3Si5. In the latter system, a possible formation of a
ferromagnetic ground state, which usually tends to destroy SC, has been
excluded by our calculations.
