Unveiling the pressure-induced physical variations in Cs₂SnBr₆ and Cs₂SnCl₆: A DFT study

This study employs the FP-LAPW method based on DFT to investigate the structural, electronic, and optical properties of Cs 2 SnBr 6 and Cs 2 SnCl 6 under a range of pressures up to 30[Formula: see text]GPa. We use the TB-mBJ functional to analyze the electronic and optical properties of the materials, while the GGA–PBEsol is employed to study their structural properties. Applying pressure causes a decrease in the unit cell volume and lattice constant of the double perovskites. At zero pressure, both Cs 2 SnBr 6 and Cs 2 SnCl 6 exhibit a direct bandgap. The bandgaps of both the materials decrease as the pressure increases from 0[Formula: see text]GPa to 20[Formula: see text]GPa but slightly increase for the increase in pressure from 20[Formula: see text]GPa to 30[Formula: see text]GPa. The DOS analysis conducted at 0[Formula: see text]GPa and 30[Formula: see text]GPa demonstrates a decrease in the number of states per[Formula: see text]eV as the pressure increases, along with an increase in bandwidth and a shift of the peaks toward negative energy. The electron density contours exhibit the presence of both covalent and ionic bonds at zero pressure, whereas at a pressure of 30[Formula: see text]GPa, the covalent bond strength is enhanced. Optical properties of Cs 2 SnBr 6 and Cs 2 SnCl 6 were investigated over a pressure range of 0–30[Formula: see text]GPa and a photon energy range of 0–10[Formula: see text]eV. With increasing pressure, the initial peak in these parameters was red-shifted due to a decrease in bandgap energy, while the remaining peaks blue-shifted due to the broadening of conduction and valence bands.