Multiphysical properties and stability of γ-CaSO4 from first-principles calculations

Although there is increasing interest in the γ -CaSO 4 polymorph of calcium sulfate, there is still a lack of both experimental and DFT studies that examine the electronic, thermal, optical, and stability-related properties of γ -CaSO 4 . The essential characteristics are crucial for obtaining insights that may reveal its potential applications. The present work utilizes density functional theory (DFT) and ab initio molecular dynamics (AIMD) to investigate the structural, stability, electronic, thermal, and optical properties of γ -CaSO 4 . The structure crystallizes in a hexagonal lattice with the P 6 2 22 space group. Analyses of formation energy and phonon band structure show that the structure exhibits both energetic and dynamic stability, while the AIMD simulation results confirm its thermal stability. The structure demonstrates a direct band gap of 8.55 eV, assessed using the HSE06 exchange–correlation functional, revealing insulating properties. Total and partial density of states are calculated to investigate the contribution of different atomic orbitals to the electronic structure. Thermal properties indicate that γ -CaSO 4 exhibits high heat capacity, low thermal conductivity, and a low, rapidly decreasing group velocity, characterizing it as a heat barrier. The thermal properties’ results are correlated with the phonon band structure profile of the structure, which predominantly features flat bands. The phonon partial density of states further shows the atomic contributions to the vibrations within the lattice. The optical properties encompass the real and imaginary components of the dielectric function, as well as the refractive index and absorption coefficient. The values of the static dielectric constant further verify that γ -CaSO 4 functions as a wide band gap insulator. The absorption spectra indicate that the structures exhibit considerable absorption in the deep-ultraviolet region. The findings highlight the potential of the structure as surface passivation layers for photoanodes, an effective heat barrier, and deep-UV and solar-blind photodetector, offering valuable insights for future investigations.