Structural, Electronic and Optical Properties of Cu₂GeS₃. A First Principles Study

In this paper, we have performed first-principles calculations on the structural and optoelectronic properties of Cu₂GeS₃ compound in the Cc and Imm2 structures. We have applied the linear augmented plane wave method for all electrons (FPLAPW), which is based on density functional theory (DFT) by using the local density approximation (LDA) and the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA). In addition, the modified Becke Johnson Tran and Blaha potential (TB-mBJ) combined with the Hubbard potential (U), which successfully corrects the band gap problem.

The structural properties such as lattice parameter, compressibility modulus and its derivative for Cu₂GeS₃-Cc are in good agreement with the available data, but for Cu₂GeS₃-Imm₂ there is no research work in the literature. The band structure results show that the Cu₂GeS₃-Cc compound has a direct gap (Γ-Γ) and that Cu₂GeS₃-Imm₂ is a metal.

The optical properties are calculated by determining the real and imaginary parts of the dielectric function ε(ω), the absorption coefficient, the reflectivity and the refractive index. These results indicate that these alloys are very useful for UV photo catalysis applications.