Density Functional Theory Study of ZnIn2S4 and CdIn2S4 Polymorphs Using Full-Potential Linearized Augmented Plane Wave Method and Modified Becke-Johnson Potential

ZnIn2S4 and CdIn2S4 are ternary sulfide semiconductors with attracting photoelectric and catalytic properties, which are closely related with their band structure. The full-potential linearized augmented plane wave (FP-LAPW) method is used to calculate the band structures of cubic and hexagonal polymorphs of ZnIn2S4 and CdIn2S4. Among the four systems studied, the hexagonal CdIn2S4 structure with a space group P6(3)mc (No. 186) is newly predicted, and the phonon calculation shows that its structure is dynamically stable. Owing to the well-known bandgap underestimation problem of local density approximation (LDA) and generalized gradient approximation (GGA), the effects of Hubbard model and modified Becke-Johnson (mBJ) potential to band structure are investigated. The calculated outcomes of cubic ZnIn2S4 and cubic CdIn2S4 with mBJ-GGA + U are in good agreement with the experimental data. For hexagonal ZnIn2S4, it is shown that electronic states in high valence bands and low conduction bands have different components. The origin of discrepancy between the theoretical bandgap of hexagonal ZnIn2S4 and experimental value obtained from optical absorption measurement is discussed based on the spatial separation of electron and hole states and optical transition probability.