Electronic properties and optical response of triangular and hexagonal MoS₂ quantum dots. A DFT approach

The energy states of triangular and hexagonal MoS₂ quantum dots are studies with the use of density functional theory, varying the dot size. The system edges are assumed to be passivated with sulfur-hydrogen atoms. In each case, spin-up and spin-down polarizations are investigated via the calculation of the energy gaps, density of states and the interband optical response. The structures are found to be small gap semiconductors. In addition, from the calculated real and imaginary parts of the dielectric function the static index of refraction and the so-called energy loss are evaluated. The effect of the particular dot geometry on the physical quantities under study is specially discussed. It is found that the specific triangular configuration with a total of 42 atoms in the border exhibits a very small energy bandgap associated with the spin-up polarization, which leads to a significant deviation of the value of the related static index of refraction, compared with the remaining structures investigated. From the first-principles calculation it has been also possible to evaluate the spin-polarization and estimate the total magnetic moment, which ranges from ∼2μ_B to ~14μ_B, depending on the dot size and geometry.