Lithium halide monolayers: Structural, electronic and optical properties by first principles study Mandana Safari a , Pegah Maskaneh a , Atousa Dashti Moghadam a , Jaafar Jalilian b,n a Physics Department, Razi University, Kermanshah, Iran b Young Researchers and Elite Club, Kermanshah Branch, Islamic Azad University, P.O. Box 67149-67346, Kermanshah, Iran HIGHLIGHTS  Structural optimizing represents that unlike graphene-like structures, the cubic face structure is more favor- able for alkali halide 2D structures.  Nonbonding electron pairs cause a planar buckling for all compounds.  Electronic calculations show that all compounds have an indirect energy gap.  All compounds are optically trans- parent in the visible spectrum range. GRAPHICAL ABSTRACT article info Article history: Received 12 October 2015 Received in revised form 27 December 2015 Accepted 19 January 2016 Keywords: Alkali halide Optical transition 2D monolayer Density functional theory abstract Using first principle study, we investigate the structural, electronic and optical properties of lithium halide monolayers (LiF, LiCl, LiBr). In contrast to graphene and other graphene-like structures that form hexagonal rings in plane, these compounds can form and stabilize in cubic shape interestingly. The type of band structure in these insulators is identified as indirect type and ionic nature of their bonds are illustrated as well. The optical properties demonstrate extremely transparent feature for them as a result of wide band gap in the visible range; also their electron transitions are indicated for achieving a better vision on the absorption mechanism in these kinds of monolayers. & 2016 Elsevier B.V. All rights reserved. 1. Introduction Alkali halides known as ionic compounds are characterized by their highly crystalline nature, high melting points and strong miscibility in polar media [1,2]. These materials can be considered as prototype insulator materials with great technological im- portance [3–5]. For many years, thermodynamic, elastic, structural and electronic properties of them have been investigated com- prehensively. The effect of defects in these compounds has been presented too [6,7]. Also band structure investigations reveal these compounds are recognized as wide-gap insulators that demonstrate their optical transparency in the visible region of the electromagnetic spectrum [8]. This transparency feature, espe- cially in LiF, in high compression makes this material a suitable choice for versatile window material through which to carry out wave profile measurements for shock compression experiments [9]. These compounds generally crystallize in both B1 (NaCl-type) and B2 (CsCl-type) structures. Their phase transitions have been classified as pressure and temperature dependence in first-order kind [7,10]. On the other hand, studying the role of electronic correlation on the boundary between localized and delocalized electronic states become possible through energy level investiga- tion, due to their electronic states kind. Their applications for a range of optical applications are significant besides the interaction mechanisms between the electronic and geometric structure can Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physe Physica E http://dx.doi.org/10.1016/j.physe.2016.01.025 1386-9477/& 2016 Elsevier B.V. All rights reserved. n Corresponding author. E-mail address: jaafarjalilian@gmail.com (J. Jalilian). Please cite this article as: M. Safari, et al., Physica E (2016), http://dx.doi.org/10.1016/j.physe.2016.01.025i Physica E ∎ (∎∎∎∎) ∎∎∎–∎∎∎