This work presents a first-principles investigation of the structural, electronic, optical, and thermodynamic properties of Pb-free cubic LiInI3 perovskite using density functional theory (DFT). Structural optimization confirms the stability of the cubic Pm–3 m phase with an optimized lattice constant of 6.19 Å and an equilibrium volume of 240.66 Å3. The negative formation energy (Ef) (− 0.63 \(\frac{eV}{Atom}\) ) and bulk modulus (B) of 17.68 GPa indicate thermodynamic stability and a mechanically soft but stable lattice. Electronic band structure calculations reveal that LiInI3 is a direct-band-gap semiconductor with a fundamental band gap of 0.42 eV at the R symmetry point, while density of states (DOS) analysis shows that the valence-band maximum (VBM) is mainly dominated by I-p orbitals and the conduction-band minimum (CBM) by In-s/p states. Optical calculations demonstrate a static refractive index of approximately 2.1, strong ultraviolet (UV) absorption with a pronounced absorption peak near 13 eV, and a negative real dielectric response at high photon energies, indicating plasmonic behavior. Thermodynamic properties calculated within the quasi-harmonic Debye (QHD) model reveal smooth pressure- and temperature-dependent variations in volume, free energy, heat capacity, entropy, and Debye temperature (ΘD) over the investigated ranges (0–1000 K and 0–2.5 GPa), confirming excellent vibrational and thermal stability without phase transitions. These findings establish LiInI3 as a structurally stable, environmentally friendly, Pb-free perovskite with promising potential for future optoelectronic, photonic, and UV-device applications.
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