  Thermoelectric properties of the system La$_2$NiO$_{4+\delta}$ have been
studied ab initio. Large Seebeck coefficient values are predicted for the
parent compound, and to some extent remain in the hole-doped metallic phase,
accompanied of an increase in the conductivity. This system, due to its layered
structure would be a suitable candidate for an improvement of its
thermoelectric figure of merit by nanostructurization in thin films, that has
already been shown to increase the electrical conductivity ($\sigma$). Our
calculations show that in the region around La$_2$NiO$_{4.05}$ the system has a
large thermopower at high temperatures and also a substantially increased
$\sigma$. Films grown with this low-doping concentration will show an optimal
relationship between thermopower and $\sigma$. This result is obtained for
various exchange-correlation schemes (correlated, uncorrelated and
parameter-free) that we use to analyze the electronic structure of the
hole-doped compound.
