Orbital characteristics and Oscillator strength in bulk, bilayer, and monolayer MoS2: A comparison study

Abstract

Abstract In this article, the orbital characters and the oscillator strength of MoS2 in the bulk, monolayer, and bilayer structures have been studied and compared. The orbital characters are key parameters in determining the distribution and specifications of electrons in materials. The oscillator strength is also a quantity that represents the probability of electric dipole transitions. Here, the calculations of these parameters have been performed using the pseudopotential method based on density functional theory with generalized gradient approximation. For the bilayer structure, the calculations are based on the van der Waals corrected DFT. Using the results of the partial density of states obtained from the density functional theory, the orbital characters of all three structures are extracted. In addition, the oscillator strength has been derived from the matrix elements of the momentum operator using the first principles method. The results of orbital character and oscillator strength for bilayer and bulk are similar and completely different from those of the monolayer. Such similarities in orbital character and oscillator strength for the bulk and bilayer could be related to the fact that they belong to the point groups with the same symmetry characteristics. Accordingly, the difference in orbital character and oscillator strength of the monolayer MoS2 could be because the monolayer has a point group with different symmetry characteristics. Both bulk and bilayer structures belong to the D6h and D3d points groups with inversion center symmetry called centrosymmetric, and the monolayer belongs to the D3h points group without the inversion symmetry, named noncentrosymmetric.