  The work carried out first-principles calculations within the framework of
density functional theory to study the structural stability of the CsSnI3
compound and the influence of phase transitions on their electronic and optical
properties. Using the GGA and SCAN functionals, the relaxed structures of the
CsSnI3 phases were obtained and their geometric characteristics were assessed.
Using the Phonopy code based on VASP, calculations of phonon and thermodynamic
properties were performed, and the temperatures of phase transitions of CsSnI3
were determined. Electronic properties and Fermi level shifts as a result of
phase transformations of CsSnI3 were assessed using the HSE06 functional and
machine learning prediction. The values of the complex dielectric constant and
the refractive index of all phases of the CsSnI3 were determined.
