Optics and Photonics Journal, 2011, 1, 1-4 doi:10.4236/ opj.2011.11001 Published Online March 2011 (http://www.SciRP.org/journal/opj) Copyright © 2011 SciRes. OPJ Investigation of the Optical Properties of CdBr 2 Hamdollah Salehi, Nastaran Asareh Department of Physics, Shahid Chamran University of Ahvaz, Ahvaz, Iran E-mail: salehi_h@sua.ac.ir Received Feburary 13, 2011; revised Feburary 28, 2011; accepted March 7, 2011 Abstract The optical properties of CdBr 2 were studied by first principle using the density functional theory. The di- electric functions and optical constants are calculated using the full potential-linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA). The theoretical calculated optical properties and energy Loss (EEL) spectrum yield a static refractive index of 2.1 and a plasmon ener- gy of 13eV for hexagonal phase. The results, in comparison with the published data, are in good agreement with the experimental and previous theoretical results. Keywords: Optical Properties, CdBr 2 , WIEN2k, FP-LAPW, DFT, GGA 1. Introduction Cadmium halogenides are widely uses as radiations. The lattice of these complicated crystals are strongly anisotropic. The CdBr2 structure is of the CdCl 2 type, namely, the rhombic lattice with 5 3d D symmetry [1]. Cadmium bromide Crystallise with layer structures in which band- ing within the layer is strong with a large ionic contribu- tion, while bonding between the layers is weak. The ba- sic structure of these materials is an infinite hexagonal sheet of Cd atoms sandwiched between two similar sheets of halogen atoms, the Cd atoms being Octahe- drally coordinated. These three-sheet sandwiches (or layers) are then stacked to form the three-dimensional compound. Because of the weak binding between the layers, different stacking sequences represent only slight differences in total energy and so several such sequences are possible. There is relatively little information availa- ble about the electronic and optical properties of the cadmium halides as a whole. Band structure calculations have recently been made for CdI, (McCanny et al 1977, Bordas et al 1978, Robertson 1979). Optical experiments in the main have been concerned with the strong excitons exhibited by all three materials [2]. Cadmium bromide is known as a photochromic crystal and is widely used as window for Infrared applications [3]. In the present work the optical properties of CdBr 2 have been studied using the full potential linearized augmented plane wave method (FP-LAPW). The results, in compari- son with the published data, are in good agreement with the experimental and previous theoretical results. 2. Method of Calculation Calculation of the optical properties, of CdBr 2 were car- ried out with a self-consistent scheme by solving the Kohn-Sham equation using a FP-LAPW method in the framework of the DFT along with the GGA method [4,5] by WIEN2k package [6]. In the FP-LAPW method, space is divided into two regions, a spherical “muf- fin-tin” around the nuclei in which radial solutions of Schrödinger Equation and their energy derivatives are used as basis functions, and an “interstitial” region be- tween the muffin tins (MT) in which the basis set con- sists of plane waves. There is no pseudopotential ap- proximation and core states are calculated selfconsis- tently in the crystal potential. Also, core states are treated fully relativistically while valence and semi-core states are treated semi-relativistically (i.e. ignoring the spin orbit coupling). The cut-off energy, which defines the separation of the core and valance states, was chosen as –6 Ryd. The complex dielectric tensor was calculated, in this program, according to the well-known relations [7].     2 α β c v 2 2 c,v 4πe Im dk c |p |v v |p |c δε ε ω m ω          k k k k k k (1)     2 2 0 Im 2 Re π P d                     (2) and the optical conductivity is given by: