Cu-based chalcopyrite semiconductors (I–III–VI₂) are leading candidates for thin-film photovoltaics, thermoelectrics, and nonlinear optics due to their tunable optoelectronic properties and radiation hardness. This work presents a combined first-principles and empirical investigation of the structural stability, cohesive energy, elastic constants, and thermal behavior of four key compounds: CuInSe₂, CuGaSe₂, CuInS₂, and CuGaS₂. Using density functional theory (DFT) within the generalized gradient approximation (GGA-PBE), we calculate equilibrium lattice parameters, cohesive energies, elastic constants, and bulk moduli. The Born-Huang stability criteria confirm mechanical stability for all compounds. Our results show negative cohesive energies (ranging from –3.82 eV/atom for CuInSe₂ to –4.56 eV/atom for CuGaS₂), indicating strong thermodynamic stability. Elastic constants systematically increase when replacing Se with S and In with Ga, with CuGaS₂ exhibiting the highest stiffness (C₁₁ = 115 GPa, B = 84 GPa). Empirical models estimate Debye temperatures (265–372 K), thermal conductivity, and elastic anisotropy. The anisotropy factors near unity (1.16–1.30) suggest nearly isotropic mechanical behavior. Sulfur-containing compounds display higher Debye temperatures and thermal conductivity due to enhanced covalent bonding. These results agree well with available experimental and theoretical data, providing a quantitative basis for designing mechanically robust chalcopyrite-based devices.

Keywords— Chalcopyrite semiconductors; Cohesive energy; Elastic constants; DFT; Mechanical stability; Thermal properties; Cu(In,Ga)(S,Se)₂; Photovoltaic materials.