  We consider strongly-correlated systems described by the multi-orbital
Hubbard model in the atomic limit and obtain exact expressions for the chemical
potential and thermopower. We show that these expressions reduce to the Heikes
formula in the appropriate limits ($k_BT \gg U$) and ($k_BT \ll U$) and obtain
the full temperature dependence in between these regimes. We also investigate
the effect of a magnetic field introduced through a Zeeman term and observe
that the thermopower of the multi-orbital Hubbard model displays spikes as a
function of magnetic field at certain special values of the field. This effect
might be observable in experiments for materials with a large magnetic
coupling.
