Effect of vacancy defects on the optoelectronic properties of 1T-TaS₂ under torsional deformation

The effects of vacancy defects and torsion on the optoelectronic properties of single-layered 1[Formula: see text]-TaS2, including the band structure, electron density difference, defect formation energy and complex dielectric function, are systematically investigated using the first-principles method based on density functional theory (DFT). The results show that vacancy defects cause relaxation of surrounding atoms leading to local distortions in the structure and changes in bond length, and the formation energy of the V[Formula: see text] system is significantly lower than theV[Formula: see text] system, which is easier to achieve the single sulfur-atom vacancy in the experiment. The vacancies system successfully opens a narrow bandgap under torsion, where the V[Formula: see text] system shows a decreasing trend in the range of 2–8[Formula: see text], increasing after 10[Formula: see text], while V[Formula: see text] systems keep increasing. Meanwhile, we found that the optical properties of 1[Formula: see text]-TaS2 monolayer are closely related to defects and torsion. The results show that the static dielectric constant, the maximum of the imaginary part, initial absorption coefficient and reflectivity of 1[Formula: see text]-TaS2 monolayer gradually increases with torsion. The spectra of vacancy systems are all elevated in the low-frequency band, indicating that the vacancy defects have improved the properties of the visible region. The significant decrease after 5 eV indicates that the torsion substantially affects the properties in the UV region.