Elastic, electronic and optical properties of cubic antiperovskites SbNCa 3 and BiNCa 3 M. Moakafi a , R. Khenata a, * , A. Bouhemadou b, * , F. Semari d , Ali H. Reshak c , M. Rabah d a Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, 29000 Mascara, Algeria b Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University of Setif, 19000 Setif, Algeria c Institute of Physical Biology, University of S. Bohemia, Institute of System Biology and Ecology Academy of Sciences, Nove Hrady 373 33, Czech Republic d Physics Department, Faculty of Science, University of Sidi-Bel-Abbès 22000, Algeria article info Article history: Received 8 April 2009 Accepted 15 May 2009 Available online 16 June 2009 PACS: 71.15.Ap 71.15.Mb 71.20.Lp 74.25.Gz 78.20.Ci Keywords: Antiperovskite FP-APW+lo Elastic properties Electronic structure Optical properties abstract The structural, elastic, electronic and optical properties of ANCa 3 (A = Sb and Bi) compounds with the cubic antiperovskite structure have been investigated using a full relativistic version of the full-potential augmented plane-wave plus local orbitals method based on the density functional theory, in conjunction with both the local density approximation and the generalized gradient approximation (GGA). For reli- able description of energy band gap values, another form of GGA developed by Engel and Vosko (GGA- EV) has been applied. The calculated structural properties, namely equilibrium lattice constant, bulk modulus and its first-order pressure derivative, are in good agreement with the available theoretical and experimental results. We have determined the full set of first-order elastic constants, shear modulus, Young’s modulus, Poisson’s ratio and Debye temperature of these compounds. Band structures reveal that these compounds are direct energy band gap semiconductors. The analysis of the site and momentum projected densities shows that bonding is of covalent–ionic nature. The obtained energy band gap values using GGA-EV are larger than those obtained within LDA and GGA. The optical constants, including the dielectric function, optical reflectivity, refractive index and electron energy loss, are calculated for radi- ation up to 15 eV. This is the first quantitative theoretical prediction of the optical properties for these compounds that requires experimental confirmation. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction The ternary nitrides or carbides with the cubic antiperovskite structure belong to a class of materials with the general formula AXM 3 , where A is a main group III–V elements, X is a carbon or nitrogen, and M is a transition metal [1]. It has been found that these antiperovskites display a variety of interesting properties such as a giant magnetoresistance [2], nearly zero temperature coefficient of resistivity [3] and depending on their chemical com- position, can also display a wide variety of physical properties ranging from semiconducting to magnetic and superconducting properties [1,4–7]. The ternary calcium nitrides ANCa 3 (A = Sb and Bi), belonging to the antiperovskite family compounds, crystallize in the cubic structure with space group Pm3m (# 221). The A atoms are posi- tioned at the (0; 0; 0) positions, the N atoms at (0.5; 0.5; 0.5) and Ca atoms at (0; 0.5; 0.5). Experimentally, Chern and co-workers [8] reported the synthe- sis of ANCa 3 (A = P, As, Sb and Bi) by mixing and pressing Ca 3 N 2 powders and group V elements into a pellet and subsequently heating the pellet at 1000 °C in flowing dry N 2 gas. Shortly after, Papaconstantopoulos and Pickett [9] studied the electronic struc- ture and bonding properties of BiNCa 3 and PbNCa 3 compounds, using the augmented plane-wave method. Few years after, Vansant and collaborators [10] investigated the structural and electronic properties under high pressure of AsNCa 3 and BiNCa 3 , using the ab initio norm conserving Troullier pseudo-potential method. Recently, Beznosikov [11] studied the structural properties of some antiperovskite nitrides, using a crystal-chemical analysis. More recently, Haddadi and co-workers [12] studied the elastic proper- ties under pressure effect of these compounds, using the plane- wave pseudo-potential method. Despite these reported results, there is still a lack of information about some of their physical properties. No calculations on the electronic band structure of SbNCa 3 have been reported yet. Nei- ther experimental nor theoretical details regarding the optical properties of SbNCa 3 and BiNCa 3 compounds are available. There- fore, we think it is worthwhile to perform calculations for these properties, using the full-potential augmented plane-wave plus 0927-0256/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.commatsci.2009.05.011 * Corresponding authors. Tel.: +213 36 92 51 28; fax: +213 36 92 51 01. E-mail addresses: khenata_rabah@yahoo.fr (R. Khenata), a_bouhemadou@ yahoo.fr (A. Bouhemadou). Computational Materials Science 46 (2009) 1051–1057 Contents lists available at ScienceDirect Computational Materials Science journal homepage: www.elsevier.com/locate/commatsci