Electronic and optical properties of BaTe, BaSe and BaS from first principles

Electronic and optical properties of barium chalcogenide compounds BaX (X = S. Se and Te) in NaCl crystal structure are calculated using the band structure results obtained through the full potential linearized augmented plane wave (FP-LAPW) method. The exchange correlation potential is treated by the generalized gradient approximation. The real and imaginary parts of the dielectric function epsilon(omega), the optical absorption coefficient 1(omega), the reflectivity R(omega) and the energy loss function are calculated. The calculated results show good agreement with the available experimental results, particularly in the low-energy region of the spectra. Furthermore the interband transitions responsible for the structures seen in the spectra are specified. It is shown that the chalcogen p states and Ba 5d states play a major role in optical transitions as initial and final states, respectively. The effect of the spin-orbit coupling on the optical properties is also investigated and found to be significant, especially in high-energy regions. (c) 2005 Elsevier B.V. All rights reserved.