Journal of Alloys and Compounds 503 (2010) 10–18 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Electronic and optical properties of alkali metal selenides in anti-CaF 2 crystal structure from first-principles S.M. Alay-e-Abbas a , N. Sabir a , Y. Saeed b , A. Shaukat c,∗ a Department of Physics, GC University, Allama Iqbal Road, Faisalabad 38000, Pakistan b Institute of Physical Biology, South Bohemia University, Nove Hrady 37333, Czech Republic c Department of Physics, University of Sargodha, Sargodha, Pakistan article info Article history: Received 8 February 2010 Received in revised form 1 May 2010 Accepted 3 May 2010 Available online 11 May 2010 Keywords: Alkali metal selenides First-principles calculations FP-LAPW Electronic and optical properties Generalized gradient approximation abstract We have performed FP-LAPW calculations in the framework of density functional theory (DFT) to compute ground-state electronic and optical properties of alkali metal selenides M 2 Se [M: Li, Na, K, Rb] in anti-CaF 2 crystal structure. The generalized gradient approximation (GGA) parameterization schemes proposed by Wu and Cohen (WC) and Engel and Vosko (EV) have been utilized for these calculations and some trends in the electronic properties of alkali metal selenides have been analyzed in the light of available theoretical and experimental data of other group IA–VI crystals. Electronic density of states for these compounds has been obtained to elucidate contribution from different anion and cation states to the electronic structure. Optical properties such as complex dielectric function ε(ω), absorption coefficient I(ω), refractive index n(ω), extinction coefficient k(ω) and reflectivity R(ω) for incident photon energy up to 35 eV and energy- loss functions have been predicted for M 2 Se compounds. Various interband transitions and the possible contributions of the cation and anion states to these transitions have been presented. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The oxides (M 2 O) and chalcogenides (M 2 Ch) of alkali metals [M: Li, Na, K, Rb; Ch: S, Se, Te] constitute a crystalline family that has shown great technological usefulness in devices requiring high ionic conductivity and large fundamental energy band gaps. Apart from being used in power sources, fuel cells, gas-detectors and ultra violet space technology devices, these ionic compounds also play important role in the development of photocathode, in support- ing catalytic reactions and enhancing oxidation of semiconductor surfaces [1–8]. At room temperature these compounds crystallize into a stable anti-CaF 2 (anti-fluorite) structure type [9–10] (space group Fm ¯ 3m). The CaF 2 (calcium fluoride) compound has a basic crystalline structure that consists of a face-centered cubic pack- ing of Ca cations, with F anions located in all the Ca tetrahedral. Whereas, the anti-morphous to the CaF 2 structure has exchanged positions of the cations and anions, and is known as the anti-fluorite type structure. In the M 2 Se [M: Li, Na, K, Rb] compounds, the metal atoms (M) are located at (0.25; 0.25; 0.25) and (0.75; 0.75; 0.75) and the selenium atoms (Se) are located at (0; 0; 0) as shown in Fig. 1. ∗ Corresponding author. Tel.: +92 48 9230618; fax: +92 48 9230671. E-mail address: schaukat@gmail.com (A. Shaukat). Unlike the oxide and sulfide compounds of this crystal fam- ily, the selenides of alkali metals have received less investigative attention from researchers towards their electronic and optical traits. Most of the research work for alkali metal selenides has been confined to studying the structural properties of these mate- rials [11–14]. However, no theoretical and experimental account of the electronic and optical properties of these materials was avail- able in literature until recently when Eithiraj et al. [15] utilized the Tight-Binding Linear Muffin-Tin Orbitals (TB-LMTO) method to investigate ground-state and under compression electronic behav- ior of selenides and tellurides of Li, Na and K. In order to understand and enhance our knowledge of the elec- tronic and optical properties of these materials and motivated by their inalienable importance among binary crystals, we have car- ried out self-consistent density functional calculations within the generalized gradient approximation (GGA) using the Full Potential Linearized Augmented Plane Wave (FP-LAPW) method. Calculated ground-state structural properties of the aforementioned crystals have been compared with available theoretical and experimental data. Moreover, features of the electronic band structures and opti- cal parameters of alkali metal selenides have been analyzed in the light of available theoretical and experimental data of other group IA–VI crystals. The results for M 2 Se compounds presented in this paper may provide reference for future experimental as well as the- oretical studies related to these ionic materials and their intricate compounds. 0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.05.014