First‐Principles Investigation of Structural, Mechanical, and Optoelectronic Properties of Ca ₃ PI ₃

This article presents a study of the structural, electronic, optical, and mechanical properties of a cubic perovskite‐type Ca ₃ PI ₃ compound using density functional theory within the WIEN2k simulation package, through the PBEsol exchange–correlation functional. The lattice constant of optimized structure is 6.10 Å, whereas the bulk modulus of 35.00 GPa demonstrates that the material has a relatively moderate structural rigidity. The electronic band structure shows that Ca ₃ PI ₃ possesses a direct bandgap of 1.32 eV; therefore, this compound may be utilized for optoelectronic applications. The computed elastic constants were found to meet the Born–Huang stability conditions and confirm stability against homogeneous elastic deformation, while the calculated B/G ratio and Poisson's ratio indicate ductile behavior of Ca ₃ PI ₃ . In contrast, phonon calculations reveal dynamical instability of the ideal cubic phase at 0 K, suggesting stabilization through finite‐temperature lattice dynamics. The optical characteristics of Ca ₃ PI ₃ , namely, the high‐frequency electronic dielectric constant, ε _∞  = 6.3, the zero‐frequency refractive index, n (0) = 2.5, as well as the low reflectivity (18%) and strong optical absorption, indicate the potential of Ca ₃ PI ₃ for low‐loss and UV‐sensitive optoelectronic applications.