Abstract
We present a three-band tight-binding (TB) model for describing the low-energy physics in monolayers
of group-VIB transition metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te). As the conduction- and
valence-band edges are predominantly contributed by the dz2 , dxy, and dx2−y2 orbitals of M atoms, the TB model
is constructed using these three orbitals based on the symmetries of the monolayers. Parameters of the TB model
are fitted from the first-principles energy bands for all MX2 monolayers. The TB model involving only the
nearest-neighbor M-M hoppings is sufficient to capture the band-edge properties in the ±K valleys, including
the energy dispersions as well as the Berry curvatures. The TB model involving up to the third-nearest-neighbor
M-M hoppings can well reproduce the energy bands in the entire Brillouin zone. Spin-orbit coupling in valence
bands is well accounted for by including the on-site spin-orbit interactions ofM atoms. The conduction band also
exhibits a small valley-dependent spin splitting which has an overall sign difference between MoX2 and WX2.
We discuss the origins of these corrections to the three-band model. The three-band TB model developed here is
efficient to account for low-energy physics in MX2 monolayers, and its simplicity can be particularly useful in
the study of many-body physics and physics of edge states.