Extrapolated Defect Transition Level in Two-dimensional Materials: The Case of Charged Native Point Defects in Monolayer Hexagonal Boron Nitride.

Defect formation energy, as well as charge transition level (CTL), play a vital role in understanding the underlying mechanism of the effect of the defects on material properties. However, the accurate calculation of charged defects, especially for two-dimensional materials, is still a challenging topic. In this paper, we proposed a simplified scheme to rescale the CTLs from the semi-local functional to the hybrid functional level, which is time-saving during the charged defect calculations. Based on this method, we systematically calculated the formation energy of four kinds of intrinsic point defects in two-dimensional hexagonal boron nitride (2D h-BN) by uniformly scaling the supercells, by which, we found a time-saving method to obtain the "special vacuum size" [ Phys. Rev. X 4 031044 (2014).]. Native defects including nitrogen-vacancy (VN), boron vacancy (VB), nitrogen atom anti-sited on boron position (NB) and boron atom anti-sited on nitrogen position (BN) were calculated. The reliability of our scheme was verified by taking V_N as a probe to conduct the hybrid functional calculation, and the rescaled CTL is within the acceptable error range with the pure HSE results. Based on the results of CTLs, all the native point defects in h-BN monolayer act as a hole or electron trap centers under certain conditions and would suppress the p-type or n-type electrical conduction of h-BN based devices. Our rescale method is also suitable for other materials for defect charge transition level calculations.