Torsional deformation modulation of the electronic structure and optical properties of molybdenum ditelluride systems doped with halogen atoms X (X = F, Cl, Br, I): a first-principles study

ContextUsing a first-principles plane-wave pseudopotential technique within the context of density-functional theory, the electronic structure and optical properties of the molybdenum ditelluride system doped with halogen atoms X (X = F, Cl, Br, I) were investigated. The electronic structure, density of states, charge transfer, and optical properties of halogen atom X doped on MoTe2 monolayer are systematically calculated and analyzed. It shows that the Fermi energy level is shifted upward after doping with halogen atoms. With F-MoTe2 doping, the geometrical distortion is the most pronounced, the charge transfer number is the highest, and the semiconductor shifts from a direct band gap to an indirect band gap. When the torsional deformation is between 1 degrees and 5 degrees, the F-doped MoTe2 system stays an indirect band gap semiconductor and transitions to quasi-metal at 6 degrees. It is shown that the torsional deformation can modulate the electronic properties of the doped structure and realize the semiconductor-metal transition.Optical propertiesThe F-doped system has a strong absorption peak reflection peak after torsion, and with the increase of torsion angle, the absorption peak is red-shifted, and the reflection peak is blue-shifted. Moreover, the absorption and reflection peaks start to decrease with the rise of the torsion angle.MethodsWe apply the generalized gradient approximation plane-wave pseudopotential technique based on Perdew-Burke-Ernzerhof (PBE) generalized functions, under the first principles of the density-functional theory framework. The overall optimization of the intrinsic molybdenum ditelluride structure and the halogen atom X-doped molybdenum ditelluride structure was carried out. Then, the F-doped molybdenum ditelluride system was selected for torsional deformation with torsion angles from 1 degrees to 6 degrees for computational analysis.Specific methodTo make the presentation more accessible, the atoms in the F-doped molybdenum ditelluride system were colored differently. The pink chain edge atoms were first reversed by theta degrees. Then, the blue chain edge atoms were reversed by theta degrees in the other direction. The middle row of atoms was adjusted accordingly to the different twisting angles of the two sides by doing the corresponding torsion with the torsion angle theta degrees/2 and fixing the individual atoms. The calculation employs the Monkhorst-Pack particular K-point sampling method. The 3 x 3 x 1 inverted-space K-point grid is utilized for material structure optimization calculations in each model, and the 9 x 9 x 1 K-point grid is used for material electronic structure calculations. A 15 angstrom vacuum layer is put on the crystal surface of vertical monolayer molybdenum ditelluride supercells to avoid interactions with adjoining cells.

Automated summary

In this study, the electronic structure and optical properties of the molybdenum ditelluride system doped with halogen atoms were investigated using a first-principles plane-wave pseudopotential technique within the context of density-functional theory. The results show that the Fermi energy level is shifted upward after halogen atom doping and the electronic properties can be modulated by torsional deformation, leading to a semiconductor-metal transition.