Theoretical study of M₆X₂ and M₆XX' structure (M = Au, Ag; X,X' = S, Se): Electronic and optical properties, ability of photocatalytic water splitting, and tunable properties under biaxial strain

MoS_2, a transition metal dichalcogenide (TMDC), has attracted significant amount of attention due to its direct bandgap, tunability and optical properties. Recently, a novel structure consisting of MoS_2 and noble metal nanoclusters has been reported. Inspired by this, first principle calculations are implemented to predict the structures of M_6X_2 and M_6XX' (M= \rm Au, Ag; X, X' =\rm S, Se). The calculated bandgap, band edge position, and optical absorption of these structures prove that the silver compounds (Ag_6X_2 and Ag_6XX') have great potential for catalytic water splitting. In addition, biaxial strain (tensile strain and compressive strain) is applied to adjust the properties of these materials. The bandgap presents a quasi-linear trend with the increase of the applied strain. Moreover, the transition between the direct and indirect bandgap is found. The outstanding electronic and optical properties of these materials provide strong evidence for their application in microelectronic devices, photoelectric devices, and photocatalytic materials.