Comprehensive DFT study of AgBeCl₃ perovskite structural and mechanical properties, electronic, optical, thermoelectric behavior, and dynamical stability via phonon analysis

Abstract

This work presents a detailed theoretical investigation into the structural, mechanical, electronic, optical, and thermoelectric characteristics of the AgBeCl₃ perovskite material using density functional theory (DFT) within the full-potential linearized augmented plane wave (FP-LAPW) framework. Two cubic structural models were examined, showing similar lattice constants and bulk modulus values but notable differences in formation energy (∼4.85 eV), which raises concerns about previously reported data. Mechanical stability is confirmed through calculated elastic constants, with the B/G ratio and Poisson's value indicating a ductile nature. Band structure analysis using TB-mBJ and PBE-GGA approaches reveals an indirect bandgap of approximately 3.36 eV, transitioning from the M to Γ point in the Brillouin zone. This aligns with the Tauc method estimation of around 3.15 eV. The optical absorption spectrum exhibits strong interband transitions with distinct peaks at 6.22 eV and 6.47 eV. Thermoelectric performance shows potential, particularly at moderate temperatures, although high thermal conductivity at elevated temperatures may limit efficiency. Additional studies under hydrostatic pressure reveal non-linear variations in elastic moduli, with maximum values observed near 2–3 GPa. Phonon dispersion results show the presence of imaginary frequencies along several symmetry paths, suggesting possible dynamical instability and a tendency toward structural phase transitions. These findings offer the first comprehensive theoretical evaluation of AgBeCl₃, shedding light on its multifunctional properties and highlighting key issues related to its stability and synthesis.