Hüser, Falco4; Olsen, Thomas1; Thygesen, Kristian Sommer3
1 Department of Physics, Technical University of Denmark2 Center for Atomic-scale Materials Design, Center, Technical University of Denmark3 Center for Nanostructured Graphene, Center, Technical University of Denmark4 Office for Innovation & Sector Services, Administration, Technical University of Denmark
We present first-principles many-body calculations of the dielectric constant, quasiparticle band structure, and optical absorption spectrum of monolayer MoS2 using a supercell approach. As the separation between the periodically repeated layers is increased, the dielectric function of the layer develops a strong q dependence around q = 0. This implies that denser k-point grids are required to converge the band gap and exciton binding energies when large supercells are used. In the limit of infinite layer separation, here obtained using a truncated Coulomb interaction, a 45 x 45 k-point grid is needed to converge the G(0)W(0) band gap and exciton energy to within 0.1 eV. We provide an extensive comparison with previous studies and explain agreement and variations in the results. It is demonstrated that too coarse k-point sampling and the interactions between the repeated layers have opposite effects on the band gap and exciton energy, leading to a fortuitous error cancellation in the previously published results.
Physical Review B (condensed Matter and Materials Physics), 2013, Vol 88, Issue 24