First-principles investigation reveals an orthorhombic ground state in lead-free RbSrI3, demonstrating how lattice mismatch dictates structural and optoelectronic properties.
Key Points
Identify the true ground-state crystal structure of the lead-free halide perovskite RbSrI3 and resolve the microscopic origins of instability in its high-symmetry phase.
Conducted first-principles density functional theory calculations using the GGA-PBE exchange-correlation functional and projector augmented-wave method in VASP.
Evaluated energetic hierarchy, lattice dynamical stability via phonon dispersion, and finite-temperature thermodynamic stability.
Applied the HSE06 hybrid functional for electronic band gaps and performed crystal orbital Hamilton population analysis to evaluate chemical bonding.
Identified the distorted orthorhombic Cmcm phase as the true ground state, demonstrating that the ideal cubic Pm-3m phase is dynamically unstable due to soft Rb-I vibrational modes driven by an undersized Rb+ cation.
Crystal orbital Hamilton population analysis showed that octahedral tilting enhances Rb-I interactions while relieving antibonding Sr-I interactions to stabilize the orthorhombic structure.
Structural distortion enlarged the calculated band gap from 3.32 eV to 3.76 eV under GGA-PBE and from 4.34 eV to 4.77 eV under HSE06, significantly modifying the material's optical spectra.