INTERLAYER INTERACTION AND SCREENING IN MoS2

Electronic band structures and phonon bands of bulk, bilayer and monolayer MoS2 are studied by DFT and GW methods and discussed in the framework of applicability of the 2D model for layered systems. The MoS2 monolayer is found to be a direct gap semiconductor with the top of the valence band and the bottom of the conduction band at K-point. For a bulk MoS2, the bandgap, estimated within GW, agrees with the indirect bandgap obtained in experiment. However, for a MoS2 monolayer, the GW-derived gap exceeds the energy of the photoluminescence line by ~0.9 eV. In contrast, the LDA value (1.84 eV) is consistent with the position of the photoluminescence line as well as with absorption spectroscopy and photoconductivity experiments. A significant overlap of the LDA-derived electron densities (in contrast to GGA results) indicates that the interlayer interaction in MoS2 can be explained by the exchange interaction. Phonon bands, calculated for MoS2 monolayer and bilayer within LDA, are consistent with Raman spectra, thus indicating the capability of LDA to correctly describe interactions in the layered system, including the interlayer interactions usually attributed to van der Waals forces.