Electronic Structure and Optical Property of 2D MgPX3 (X = S and Se) Monolayer by Density Functional Theory

2D metal phosphorus trichalcogenides (MgPX3 ) have attracted tremendous research interests in spintronic, electrocatalytic, and photoelectronic applications due to their unique magnetic and optical properties. Herein, a systematical investigation on the electronic structures and optical properties of 2D MgPX3 (X = S and Se) monolayers is performed by density functional theory. Owing to small cleavage energy, 2D MgPX3 monolayers can be obtained by mechanical exfoliation with an excellent structure stability of 2D MgPX3 monolayers demonstrated by elastic tensor, phonon dispersion, and molecular dynamics, respectively. 2D MgPX3 behaves as a direct bandgap semiconductor with a strong optical absorption in UV range whereas a weak adsorption near the band edge, demonstrated by both single- and quasiparticle approximations. Upon analyses on transition dipole moment along with the wave function symmetry, the weak optical absorption is attributed to the parity-forbidden effect where the wave functions almost show the same parity between top valence band and bottom conduction band. The findings indicate that 2D MgPX3 monolayers hold promise as candidate materials for flexible UV photoelectronics devices and provide a theoretical insight into the optical properties of 2D semiconductors.