The interaction between vacancy defects in gallium sulfide monolayer and a new vacancy defect model

Vacancy defects are inevitable when synthesizing two-dimensional (2D) materials, and vacancy defects greatly affect the physical properties, such as magnetism and electronic properties. Currently, sufficient information is not available on whether and how the interaction of vacancy defects affects material properties and how to control these defects and their associated interaction for the development of new materials. In this study, the interaction between two adjacent vacancy defects of the gallium sulfide (GaS) monolayer is investigated using first-principles calculations based on density functional theory (DFT). The results indicate that the localized size of a Ga vacancy defect is the area within the S atoms second nearest to the neighboring vacancy defect. When the localized sizes of Ga vacancy defects intersect, a non-negligible interaction exists between the Ga vacancy defects. The interaction generally has been ignored by the traditional defect concentrations model but would affect the magnetic and electronic properties of the defective GaS monolayer. A vacancy defect cluster model (VDCM) is developed based on the system clustering method and then used to evaluate the interactions between vacancy defects. In order to check the reliability of the model, this research studies a defective MoS2 monolayer as an example and compares the band gap and density of states (DOS) calculated by using different vacancy defect models, including VDCM. The results indicate that VDCM has good accuracy relative to the traditional vacancy concentration model. This means that with the help of VDCM the properties of the defective system could be calculated more accurately considering some extent of nonuniform distribution of defects based on DFT.