Influence of different exchange correlation potentials on band structure and optical constant calculations of ZrGa 2 and ZrGe 2 single crystals A.H. Reshak a,b,⇑ , A.O. Fedorchuk c,g,⇑ , G. Lakshminarayana d , Z.A. Alahmed f , H. Kamarudin b , S. Auluck e a Institute of Complex Systems, FFPW, CENAKVA-South Bohemia University CB, Nove Hrady 37333, Czech Republic b Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis, Malaysia c Lviv National University of Veterinary Medicine and Biotechnologies, Department of Inorganic and Organic Chemistry, Lviv, Ukraine d Materials Science and Technology Division (MST-7), Los Alamos National Laboratory, Los Alamos, NM 87545, USA e National Physical Laboratory, Dr. K S Krishnan Marg, New Delhi 110 012, Saudi Arabia f Department of Physics and Astronomy, King Saud University, Riyadh 11451, Saudi Arabia g P. Sagajdachnyj Miltary University, Lviv, Ukraine article info Article history: Received 7 March 2013 Received in revised form 27 April 2013 Accepted 29 April 2013 Available online 19 June 2013 Keywords: Inorganic materials Crystal growth Electronic band structure abstract The all-electron full potential linearized augmented plane wave method was used to solve the Kohn Sham DFT equations. We have employed different approximations for the exchange correlation potentials, namely: LDA, GGA and EVGGA, and insignificant effect on the band structure and the density of states were found. Calculations show that there is a significant difference in the band dispersion with replace- ment of Ga by Ge that is attributed to the fact that in the ZrGe 2 compound Zr atom is situated at 4c site and two Ge atoms are situated at 4c site. Whereas for ZrGa 2 compound Zr is located at 4g site and the three Ga atoms are situated at 4h, 2c and 2a sites, respectively. There exists strong hybridization between the states. Moving from ZrGa 2 to ZrGe 2 has significant influence on the magnitudes and the peak posi- tions of states. The optical properties of the two compounds were studied and analyzed. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction It is well known systematization of structural types with re- spect to the coordination of the atoms of the smallest sizes [1], which gives to classify structural types by classes, groups and to establish an affinity between structural types within the same class as well as between structural types, belong to different classes. Usually these approaches are different. In this work we try to look on the behavior of the corresponding energy band gaps. To study such relations the better way is to perform the calculations for the isostructural compounds. Among the binary compounds particular interest present ha- lides, germanides, antimonides, arsenides, etc. Partially covalence bonds prevailingly form more electronegative atoms and atoms with less electronegativity usually occupy empty structural posi- tions or occupy voids in cluster layers or polyhedra formed by an- ions. Very often these atoms are characterized by shorter chemical bonds to anions. This phenomenon may be explained similarly to polyhedra Frank–Casper [2], i.e. like atomic agglomerates, where cationic electrons are shifted towards connections with anions. As a consequence the compound possessing the lowest electro- negativity for compounds of different classes at fixed structural type should be changed. As a consequence, in the Ref. [3] an at- tempt has been made to perform a classification of structural types with respect to the atoms with maximal sizes. Following the rea- sons presented above in the present work we explore the band structure performed within a framework of DFT method with dif- ferent exchange correlation potentials: LDA, GGA and EVGGA. For this reason we have chosen compounds ZrGa 2 and ZrGe 2 [4] pos- sessing the same structural fragments (Fig. 1). At the same time their electronic configuration is different from each other. The choice of the different exchange correlations approach should add to help the influence of this screening on the band structure behaviors. The quantum chemical simulations should show how sensitive they will be to such different potential screenings. To the best of our knowledge no comprehensive work neither experimental data on the optical properties or first principles cal- culations on the structural, electronic, and optical properties of ZrGa 2 and ZrGe 2 compounds have appeared in the literature. Therefore as a natural extension to previous work on ZrGa 2 and ZrGa 3 compounds [5,6] a detailed depiction of the structural, electronic, and optical properties of ZrGa 2 and ZrGe 2 using full 0927-0256/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.commatsci.2013.04.056 ⇑ Corresponding authors. Address: Institute of Complex Systems, FFPW, CEN- AKVA-South Bohemia University CB, Nove Hrady 37333, Czech Republic (A.H. Reshak). Tel.: +420 777 729 583; fax: +420 386 361 219. E-mail addresses: ft.1958@yahoo.co.uk, maalidph@yahoo.co.uk (A.O. Fedorchuk). Computational Materials Science 78 (2013) 134–139 Contents lists available at SciVerse ScienceDirect Computational Materials Science journal homepage: www.elsevier.com/locate/commatsci