Detailed DFT studies of the band profiles and optical properties of antiperovskites SbNCa 3 and BiNCa 3 M. Bilal a , Iftikhar Ahmad a,⇑ , H.A. Rahnamaye Aliabad b , S. Jalali Asadabadi c a Center for Materials Modeling and Simulations, University of Malakand, Chakdara, Pakistan b Department of Physics, Hakim Sabzevari University, Sabzevar, Iran c Department of Physics, Faculty of Science, University of Isfahan, HezarGerib Avenue, Isfahan 817446-73441, Iran article info Article history: Received 6 October 2013 Received in revised form 18 November 2013 Accepted 16 December 2013 Keywords: Antiperovskites Electronic band structure Density of states DFT Optical properties abstract Structural, electronic and optical properties of antiperovskite compounds, SbNCa 3 and BiNCa 3 , are studied by using the full-potential linearized augmented plane waves (FP-LAPW) method under the framework of density functional theory (DFT). The exchange–correlation potential is treated by local density approxi- mation (LDA), generalized gradient approximation (GGA-PBEsol) and GGA developed by Engel and Vosko (EV-GGA). Furthermore, the modified Becke–Johnson (mBJ) potential is also applied to attain reliable results for the band gaps of these compounds. The calculated lattice constants are found consistent with the experimentally measured values and other theoretical results. The band profiles show that both of these materials are direct band gap semiconductors of about 1.1 eV gap. The direct band gap nature reveals that they may be effective in optical devices and therefore the optical properties of these com- pounds like the real and imaginary parts of dielectric function, refractive index and absorption coefficient are also calculated and discussed. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Ternary carbides and nitrides having cubic antiperovskite struc- ture are emerged as promising compounds for different technolog- ical applications. These materials have gained importance as they display variety of physical properties such as giant magnetoresis- tance [1], nearly zero temperature coefficients of resistivity [2] and wide range of band gaps, from super conductor to insulator [3,4]. The general formula for these compounds is AXB 3 , where A is group III–V element, X is carbon or nitrogen and B is s–d metal [5,6]. These materials crystallize in cubic structure with space group Pm3m (#221). The A atoms are positioned at (0, 0, 0) coor- dinates, X atoms at (0.5, 0.5, 0.5) and B atoms at (0, 0.5, 0.5) of the unit cell. Chern et al. [7] reported the synthesis of ANCa 3 (A = P, As, Sb and Bi) materials by mixing and pressing Ca 3 N 2 powders and group V elements into a pellet and subsequently heating the pellets at 1000 °C in the flowing dry N 2 gas. They observed semiconducting nature for SbNCa 3 and BiNCa 3 compounds. In the same year, the electronic structure and bonding properties of BiNCa 3 and PbNCa 3 materials were studied by Papaconstantopoulos and Pickett [8] using the augmented plane-wave method. They are of the opinion that the bandgap of these compounds is very narrow, about 0.07 eV for BiNCa 3 . A few years later the structural properties of AsNCa 3 , PNCa 3 and BiNCa 3 were investigated by Vansant et al. [9] using local density approximation (LDA) and are also of the opinion that BiNCa 3 is a narrow band gap semiconductor. In a relatively re- cent studies, Haddadi et al. [10] investigated the pressure depen- dent elastic properties of ANCa 3 (A = P, As, Sb and Bi) using the plane wave pseudo-potential method, while Moakafi et al. [11] ex- plored the elastic, electronic and optical properties of SbNCa 3 and BiNCa 3 using a full relativistic version of the full-potential linear- ized augmented plane-wave plus local orbitals method based on the density functional theory. The results reported in Ref. [11] contradict the claim of the authors that ‘‘SbNCa 3 and BiNCa 3 are semiconductors in nature’’. As the figures of the band profiles presented in the article clearly show that for both materials the top of valance band crosses the Fermi level and enters into the conduction band and hence these materials are not semiconducting, which is also in disagreement with the experimental results [7]. In the present article, this anom- aly is addressed with great care using different theoretical tech- niques, based on the full potential linearized augmented plane waves (FP-LAPW) method, like local density approximation (LDA), generalized gradient approximation (GGA), Engel–Vosko GGA (EV-GGA) and modified Becke–Johnson (mBJ) potential. It is expected that the present work will not only rectify the errors in the existing theoretical work, but will also provide a realistic picture of the compounds which will be helpful in understanding 0927-0256/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.commatsci.2013.12.035 ⇑ Corresponding author. Tel.: +92 332 906 7866. E-mail address: ahma5532@gmail.com (I. Ahmad). Computational Materials Science 85 (2014) 310–315 Contents lists available at ScienceDirect Computational Materials Science journal homepage: www.elsevier.com/locate/commatsci