G0W0 Many-Body Perturbation Theory for Ground and Excited States in CsSrF3 Perovskite: First-Principles Study with Yambo

This study investigates the excited-state optical properties of CsSrF ₃ perovskite using many-body perturbation theory within the G ₀ W ₀ approximation, implemented via the Yambo code. The G ₀ W ₀ method corrects the electronic band structure, yielding accurate quasiparticle energies, while the Bethe-Salpeter equation is solved to compute optical spectra. Results show a significantly improved bandgap compared to standard DFT, aligning closely with experimental data and revealing enhanced optical absorption in the UV-visible range. The findings highlight CsSrF ₃ ’s potential for optoelectronic applications, emphasising the effectiveness of the G ₀ W ₀ approach in capturing many-body effects. This work demonstrates the power of advanced computational methods for studying perovskite materials. This comprehensive study investigates the electronic, optical, vibrational, and thermodynamic properties of CsSrF₃ perovskite insulator in both ground and excited states, employing density of states (DOS), optical conductivity, dielectric function, Raman spectroscopy, and thermodynamic analyses. The ground-state electronic structure reveals a wide bandgap (~ 10 eV) dominated by F 2p valence and Sr 4d/Cs 6s conduction states, with phonon dispersion confirming structural stability. Photoexcitation induces significant modifications, including bandgap renormalisation (~ 2 eV redshift), phonon softening (10–15% reduction in Debye temperature), and the emergence of mid-gap states attributed to excitonic and defect-related transitions. Optical properties exhibit enhanced absorption and reflectivity in the excited states, while the dielectric function and loss spectra demonstrate a plasmon redshift and broadening. Thermodynamic analyses reveal nonlinear enthalpy, enhanced entropy, and metastable free energy minima under excitation, driven by lattice anharmonicity and electronic entropy. These findings collectively elucidate the interplay between electronic excitation, lattice dynamics, and thermodynamic stability in CsSrF₃, offering insights for optoelectronic applications.