  Density functional plus dynamical mean field calculations are used to show
that in transition metal oxides, rotational and tilting (GdFeO$_3$-type)
distortions of the ideal cubic perovskite structure produce a multiplicity of
low-energy optical transitions which affect the conductivity down to
frequencies of the order of $1$ or $2$~mV (terahertz regime), mimicking
non-Fermi-liquid effects even in systems with a strictly Fermi-liquid
self-energy. For CaRuO$_3$, a material whose measured electromagnetic response
in the terahertz frequency regime has been interpreted as evidence for
non-Fermi-liquid physics, the combination of these band structure effects and a
renormalized Fermi-liquid self-energy accounts for the low frequency optical
response which had previously been regarded as a signature of exotic physics.
Signatures of deviations from Fermi-liquid behavior at higher frequencies
($\sim 100$~meV) are discussed.
