Tuning optoelectronic properties in BaNaH₃X (X = Ni, Pd, Pt) perovskite hydrides: a DFT-based analysis

Perovskite hydrides are promising candidates for optoelectronic and hydrogen-related technologies, where B-site substitution offers an effective route to tune functional properties. We investigate BaNaH₃X (X = Ni, Pd, Pt) to clarify how moving down Group 10 modifies structure-property relationships relevant to light harvesting and charge transport. All three compounds are predicted to be stable in the hexagonal P6₃/mmc phase with systematic lattice expansion from Ni to Pt. Hybrid-functional (HSE06) calculations show an indirect band gap of 1.43 eV for BaNaH₃Ni and wider gaps of 2.51 eV and 2.43 eV for BaNaH₃Pd and BaNaH₃Pt, respectively, accompanied by broader band dispersion, lower carrier effective masses, and higher estimated mobilities. The calculated optical response reveals strong visible-UV absorption, large refractive indices, energy-loss peaks near 11-12 eV, and low reflectivity over the solar-relevant range, identifying BaNaH₃Ni as a high-index hydride and BaNaH₃Pd/Pt as attractive candidates for UV/visible optoelectronic applications.

First-principles density-functional theory (DFT) calculations were carried out using CASTEP. Structural optimization and ground-state properties employed GGA-PBE with OTFG norm-conserving pseudopotentials, a 500 eV plane-wave cutoff, and a Monkhorst-Pack 6 × 6 × 6 k-point mesh. Band gaps were refined using the HSE06 hybrid functional. Carrier effective masses were extracted from the converged band structures, and frequency-dependent dielectric functions and derived optical quantities were computed within the independent-particle approximation for the optimized geometries.