DFT investigation of structural and optoelectronic properties of glassy chalcogenide CuXY2 (X = Sb, Bi; Y = S, Se, Te) molecules

Abstract The structural, electronic, spectral and optical properties of the ternary semiconducting material CuXY 2 (X = Sb, Bi; Y = S, Se, Te) are computed using the density functional theory (DFT) technique. The ground-state configurations show that these systems have distorted rhomboidal structures in singlet states. It is found that CuSbY 2 possesses higher highest occupied molecular orbital (HOMO) – lowest unoccupied molecular orbital (LUMO) energy gap than CuBiY 2 . We have employed three different levels of theory (B3LYP/LANL2DZ, relativistic effective—core potentials—CRENBL++, LANL08+) to study the electronic states. The energy gaps of these materials vary from 1.926–2.183 eV and 1.862–2.340 eV, respectively, at different levels of theory, suggesting their suitability as solar cell absorbents. DFT-based global structural descriptors are computed and analyzed with the help of vertical ionization energy and vertical electron affinity. The optical properties, such as optical electronegativity, refractive index, dielectric constant and IR and Raman activity, are studied. Our results show that the optical electronegativity of CuSbY 2 is higher than that of CuBiY 2 whereas the refractive index of CuSbY 2 is smaller than that of CuBiY 2 . The computed harmonic frequencies and maximum intensities of IR and Raman spectra decline from S to Se to Te for systems CuSbY 2 and CuBiY 2 . Our computed electrostatic potentials and other electronic properties show that CuBiY 2 systems differ substantially from CuSbY 2 due to relativistic effects on Bi.