  We theoretically study the electronic and the thermal characteristics of
Tantalum, Ta, doped Molybdenum disulfide, MoS$_2$, using density functional
theory. It has been shown that the MoS$_2$ monolayer is not a good material for
thermoelectric devices due to its relatively large band gap. We find that a Ta
doped MoS$_2$ forming a TaMoS$_2$ monolayer can be useful for thermoelectric
devices. The particular attention of this work is paid to the interaction
effect between the Ta atoms in the MoS$_2$ structure. We find that the
interaction type is repulsive. It introduces an asymmetry in the density of
states, DOS, reducing the band gap. In the presence of a strong repulsive
interaction of Ta-Ta atoms, new states in the DOS around the Fermi energy are
found leading to a reduction of the band gap. Consequently, a high Seebeck
coefficient and figure of merit are seen over a wide range of energy around the
Fermi energy. In contrast, a small reduction of the band gap and a vanishing
degeneracy of the valence and the conduction bands are observed for the case of
a weak Ta-Ta repulsive interaction leading to less promising thermoelectric
properties.
