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We present here the minimal tight--binding model for a single layer oftransition metal dichalcogenides (TMDCs) MX$_{2}$ (M--metal, X--chalcogen)which illuminates the physics and captures band nesting, massive Dirac Fermionsand Valley Lande and Zeeman magnetic field effects. TMDCs share the hexagonallattice with graphene but their electronic bands require much more complexatomic orbitals. Using symmetry arguments, a minimal basis consisting of 3metal d--orbitals and 3 chalcogen dimer p--orbitals is constructed. Thetunneling matrix elements between nearest neighbor metal and chalcogen orbitalsare explicitly derived at $K$, $-K$ and $\Gamma$ points of the Brillouin zone.The nearest neighbor tunneling matrix elements connect specific metal andsulfur orbitals yielding an effective $6\times 6$ Hamiltonian giving correctcomposition of metal and chalcogen orbitals but not the direct gap at $K$points. The direct gap at $K$, correct masses and conduction band minima at $Q$points responsible for band nesting are obtained by inclusion of next neighborMo--Mo tunneling. The parameters of the next nearest neighbor model aresuccessfully fitted to MX$_2$ (M=Mo, X=S) density functional (DFT) ab--initiocalculations of the highest valence and lowest conduction band dispersion along$K-\Gamma$ line in the Brillouin zone. The effective two--band massive DiracHamiltonian for MoS$_2$, Lande g--factors and valley Zeeman splitting areobtained.

Band nesting, massive Dirac Fermions and Valley Lande and Zeeman effects in transition metal dichalcogenides: a tight-binding model