Ab initio studies of structural, electronic, optical and thermal properties of CuAlS2 chalcopyrite

The ground-state structural, electronic, optical and thermal properties of the CuAlS2 compound in the body centered tetragonal phase have been studied employing the full potential linearized augmented plane wave plus local orbitals method based on the density functional theory. For the exchange-correlation effects we have adopted the generalized gradient approximation (GGA) approaches due to Perdew, Burke and Ernzerhof (PBE) and Engel and Vosko (EV). The optical properties such as dielectric function, loss of energy, reflection, refraction and conductivity of CuAlS2 are presented. Thermal properties such as Gruneisen parameter, volume expansion coefficient α, bulk modulus, specific heat and entropy have been studied. The direct band gap first increases then starts decreasing with the decrease in unit cell volume. The EV-GGA provides higher value of energy band gap (2.20 eV) than PBE-GGA (1.62 eV). Our obtained value of the refractive index (2.4 eV) is in excellent agreement with the experimental value (2.0-2.5 eV). The peak of maximum conductivity is located at 7.4 eV of energy. The plasma frequency ωp corresponds to the energy 12.45 eV.