Excited State Properties of Layered Two-Dimensional MSi2N4 (M = Mo, Cr, and W) Materials from First-Principles Calculations

Two-dimensional (2D) MoSi2N4 layered material successfully prepared in the experiment was shown to have good light absorption performance, although its internal mechanism is not clear. We discuss the effects of replacing Mo with W and Cr atoms, respectively, on the light absorption performance of a 2D MoSi2N4 monolayer through first-principles calculations. M-site atoms play a major role in the accumulation of electrons in MA2Z4 system materials. In the visible light region, as the excited state is higher, the number of holes that appear on the N atom layer next to the central layer decreases, whereas those appearing on the N atoms of the outermost layer at both ends increase in number, indicating the research value of Z-site atoms in MA2Z4 system. More importantly, the electrons of Si atoms in the sub-outer layer will transfer when the excitation energy is sufficient, and the Mo atoms in the center layer will obtain electrons not only from other atoms but also from themselves. Replacing Mo atoms in the monolayer of MoSi2N4 with Cr atoms can redshift the ultraviolet-visible spectrum (UV) and reduce the height of the strongest absorption peak. Simultaneously, replacing MoSi2N4 monolayer with W atoms causes the blue shift of the ultraviolet-visible spectrum.