  We report the quasiparticle energy of monolayer of molybdenum and tungsten
dichalcogenides, MX2 (M=Mo, W; X=S, Se, Te). Beyond calculating bandgaps, we
have achieved converged absolute band energies relative to the vacuum level.
Compared with the results from other approaches, the GW calculation reveals
substantially larger bandgaps and different absolute band energies because of
enhanced many-electron effects. Interestingly, our fully-converged
quasiparticle energies ratify the band-gap-center approximation, making it a
convenient way to estimate quasiparticle energy. The absolute quasiparticle
energies and band offsets obtained in this work are important for designing
heterojunction devices and chemical catalysts based on monolayer
dichalcogenides.
