First principles study of structural, elastic, electronic and optical properties of CuCl, CuBr and CuI compounds under hydrostatic pressure

We have applied the full-potential linearized augmented plane wave (FP-LAPW) method to study the structural, elastic, electronic and optical properties of copper halides CuX (X=Cl, Br, I) under high pressure using the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange and correlation potential. We have calculated the ground-state energy, the lattice constant, the bulk modulus, and its pressure derivative in both NaCl (B1) and ZnS (B3) structures. A numerical first-principles calculation of the elastic constants was used to calculate C11, C12 and C44. The pressures at which these compounds undergo a structural phase transition from ZnS type to NaCl type were calculated. Band structure, density of states and band gap–pressure coefficients in ZnS phase are also given. On the other hand, an accurate calculation of linear optical functions (refraction index and its pressure derivative, and both imaginary and real parts of the dielectric function) is performed in the photon energy range up to 11 eV. The results are compared with previous calculations and experimental measurements. We show that our calculated values compare acceptably well with values reported in the literature.