  For the thermoelectric properties of NaxCoO2, we analyze the effect of local
Coulomb interaction and (disordered) potential differences for Co-sites with
adjacent Na-ion or vacancy. The disorder potential alone increases the
resistivity and reduces the thermopower, while the Coulomb interaction alone
leads only to minor changes compared to the one-particle picture of the local
density approximation. Only combined, these two terms give rise to a
substantial increase of the thermopower: the number of (quasi-)electrons around
the Fermi level is much more suppressed than that of the (quasi-)holes. Hence,
there is a particle-hole imbalance acting in the same direction as a similar
imbalance for the group velocities. Together, this interplay results in a large
positive thermopower. Introducing a thermoelectric spectral density, we located
the energies and momenta regions most relevant for the thermopower and changes
thereof.
