In the present calculations, the exchange correlation of generalized gradient approximation (GGA) with Perdew–Wang 1991 (PW-91) functional [26] as implemented in CASTEP [27] was employed. The ionic cores are represented by ultrasoft pseudopotential for Mo and S atoms. The Mo 4p64d55 s1 electrons and S 3s23p4 electrons are explicitly treated as valence electrons. The plane-wave cutoff
AGI-6780 was set to be 500 eV and the 5 × 5 × 2 k-point mesh was utilized according to the Monkorst–Pack scheme [28]. The optimized primitive lattice constants a = 3.17 Å and c = 12.32 Å are in good agreement with other theoretical data (a = 3.17 Å, c = 12.58 Å [29]) and experimental values (a = 3.20 Å, c = 12.29 Å [30]). All structures are subjected to periodic boundary conditions utilizing a supercell geometry, where local processes are treated with (4 × 6 × 1) supercells of monolayer MoS2. The large size of the supercells separates the periodic defect images by over 10 Å, greatly reducing the artificial Coulomb interactions between them [31]. And a large vacuum layer of 12 Å added along the z direction to avoid interlayer interaction. Supercell of 72 atoms for defect-free monolayer MoS2 is
glomerulus shown in Fig. 1(a). Defective monolayer MoS2 with single Mo and S vacancy is presented in Fig. 1(b) and (c), respectively.
