  By means of first-principles calculations we study the structural and
electronic properties of a superlattice made of Sr2RuO4 and Sr3Ru2O7 ruthenate
oxides. Due to the symmetry mismatch of the two systems a significant
structural rearrangement occurs within the superlattice. We find that at the
interface the RuO6 octahedra get elongated for the Sr2RuO4 while tend to be
compressed for the Sr3Ru2O7 as compared to inner layers and the bulk phases.
The positions of the Sr-atoms in the Sr-O layers at the interface are strongly
modified and influence the alignment of the Ru atoms with respect to the planar
oxygens as well as the Ru-O-Ru in-plane bond angles. Such structural
rearrangement leads to a modification of the electronic structure close to the
Fermi level. The main changes occurring at the interface and in the inner
layers of the heterostructure are analyzed and compared with the bulk phases of
the Sr2RuO4 and Sr3Ru2O7 compounds. We show that the positions of the peaks in
the density of states close to the Fermi levels get shifted and renormalized in
the spectral weight. The balance between the renormalization of the bandwidth
of the dxy band and that of the crystal field splitting results into a minor
change of the Van Hove singularities position within the superlattice. The
effective tight-binding parameters for the 4d Ru bands are determined by means
of a maximally localized Wannier functions approach and used to discuss the
modification of the electronic structure of the superlattice with respect to
the bulk phases. Consequences on the modification of the superconducting and
metamagnetic behaviour of the superlattice with respect to the bulk phases are
discussed.
