I am having some difficulties understanding values of exciton binding energies for $\ce{MoS2}$ monolayer. In various papers:

  1. Interlayer and intralayer excitons in MoS2/WS2 and MoSe2/WSe2 heterobilayers Engin Torun, Henrique P. C. Miranda, Alejandro Molina-Sánchez, and Ludger Wirtz Phys. Rev. B 97, 245427 DOI
  2. Binding energies of exciton complexes in transition metal dichalcogenide monolayers and effect of dielectric environment Ilkka Kylänpää and Hannu-Pekka Komsa Phys. Rev. B 92, 205418 DOI

They calculate exciton binding energy as difference between optical gap and electronic band gap. For example for $\ce{MoS2}$ monolayer exciton A lies around 1.85 eV. They use gw band gap around 2.35,2.40 to calculate A exciton binding energy. But in reality $\ce{MoS2}$ monolayer has around 1.9 eV experimental band gap.

The GW method is known to overestimate band gap of $\ce{MoS2}$ monolayer. In this case it’s binding energy should be around zero; can anyone explain this discrepancy?

Also, in the below paper they use another value of band gap to estimate exciton binding energy even though they have a smaller band gap they estimated with fitting:

  • Ermolaev, G.A., Stebunov, Y.V., Vyshnevyy, A.A. et al. Broadband optical properties of monolayer and bulk MoS2. npj 2D Mater Appl 4, 21 (2020). DOI


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