Published: March 04, 2011 r2011 American Chemical Society 2836 dx.doi.org/10.1021/jp111382h | J. Phys. Chem. B 2011, 115, 2836–2841 ARTICLE pubs.acs.org/JPCB First-Principles Calculations of Structural, Elastic, Electronic, and Optical Properties of Perovskite-type KMgH 3 Crystals: Novel Hydrogen Storage Material Ali H. Reshak,* ,†,‡ Mikhail Y. Shalaginov, § Yasir Saeed, † I. V. Kityk, || and S. Auluck ^,# † Institute of Physical Biology, South Bohemia University, Nove Hrady 37333, Czech Republic ‡ School of Microelectronic Engineering, University Malaysia Perlis (UniMAP), Block A, Kompleks Pusat Pengajian, 02600 Arau Jejawi, Perlis, Malaysia § School of Electrical and Computer Engineering, Purdue University, West Lafayette, 47907 Indiana, United States ) Electrical Engineering Department, Technical University of Czestochowa, Al.Armii Krajowej 17/19, Czestochowa, Poland ^ Physics Department, Indian Institute of Technology Kanpur, Kanpur (UP) 208016, India # National Physical Laboratory Dr. K S Krishnan Marg, New Delhi 110012, India 1. INTRODUCTION In recent years, one can observe an enhanced interest to groups I-III of the periodic table, for example, K, Li, Na, Mg, Ba, Sr, and Al, to form different types of complex hydrides that are interesting for the use as potential hydrogen storage materials because of their light weight. Today a lot of research activity is in progress with the aim to identify new materials with high hydrogen content and suitability to functionalize at low operating temperature. Perovskite hydrides ABH 3 are gaining much interest because of cubic structure and presence of lightweight elements like CsCaH 3 , RbCaH 3 , KMgH 3 , BaLiH 3 , and SrLiH 3 . 1-4 Mg-based phases receive particular attention because of lightweight and low cost production. Recently, a number of theoretical studies were carried out for structural and electronic properties in different phases of MMgH 3 (M = Li, Na, K, Rb, Cs). 5,6 For hydrides, owing to the complexity in structural arrangements and difficul- ties involved in establishing hydrogen positions by X-ray diffrac- tion methods, structural information is limited. 7 However, most of these materials are not well-described and thermodynamic data are absent. 8 Some of theoretical results are available only for the stability of these perovskite hydrides XLiH 3 (X = Ba and Sr) 9 and XCaH3 (X = Cs and Rb) 10 under pressure. But for Mg-based perovskite hydride KMgH 3 , no experimental or theoretical data for phase stability related to hydrogen positions are available. Keeping these points in view, we focus on stability of perovskite- type KMgH 3 according to different hydrogen positions and investigate the electronic and optical properties in that stable phase only. In the next section, we briefly describe the calculation proce- dure and give the Computational Details. In Section 3, we report and discuss our result for structural and phase stability of three different phases and then present the electronic and optical properties of only stable phase KMgH 3 . Finally, conclusions will be given in Section 4. 2. COMPUTATIONAL DETAILS Ab initio calculations for different phases of perovskite-type KMgH 3 are performed using the full potential linearized aug- mented plane wave plus local orbitals (FP-LAPW þ lo) method within a framework of density functional theory (DFT), as implemented in the WIEN2K code. 11 The generalized gradient approximation (GGA) 12 was used for the exchange-correlation potential. In these calculations, FP-LAPW þ lo basis set consisted of 3p 6 , 4s 1 states of K, 2p 6 , 3s 2 states of Mg, and 1s 1 state of H. Received: November 30, 2010 ABSTRACT: We report a first-principles study of structural and phase stability in three different structures of perovskite-types KMgH 3 according to H position. While electronic and optical properties were measured only for stable perovskite-type KMgH 3 , our calculated structural parameters are found in good agreement with experiment and other theoretical results. We also study the electronic charge density space distribution contours in the (200), (101), and (100) crystallographic planes, which gives better insight picture of chemical bonding between K-H, K-Mg-H, and Mg-H. Moreover, we have calculated the electronic band structure dispersion, total, and partial density of electron states to study the band gap origin and the contribution of s-band of H, s and p-band of Mg in the valence band, and d-band of K in the conduction band. Furthermore, optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients, optical conductivities, and loss functions of stable KMgH 3 were calculated for photon energies up to 40 eV.