Computational investigation of Rb 2 ReX 6 (X= Cl, Br, I) vacancy-ordered double perovskites: From structural stability to thermoelectric performance Mohamed El Amine a,* , Abbderrahmane Remil b , Mokhtare Saidi b , Mohamed Batouche a , Taib Seddik a , Rabah Khenata a a Laboratory of Quantum Physics of Matter and Mathematical Modeling (LPQ3M), Mascara University, mascara, Algeria b Laboratory of Organic Macromolecular Chimistry and Materials, Mascara University, Mascara, Algeria A R T I C L E INFO Keywords: Vacancy-ordered double perovskite Effective mass Electronic structure Elastic properties Seebeck coefficient Figure of merit ABSTRACT Our research, conducted using Density Functional Theory (DFT) within the WIEN2k framework, has revealed clear correlations between structural, electronic, mechanical, and thermoelectric properties of materials. These interrelationships provide valuable insights for designing materials with tailored functionalities and improved performance in targeted applications. By deepening our fundamental understanding of these materials, this approach not only enhances theoretical knowledge but also paves the way for technological innovations in fields such as semiconductors, thermoelectrics, and optoelectronics. In particular, we have extensively studied the vacancy-ordered double perovskite compounds Rb 2 ReX 6 , concentrating on their structural, electronic, me- chanical and TE properties. We are examining the compounds’ formation and cohesive energy, which allowed us to evaluate their structural stability. Compounds with high cohesive energies are known for their structural stability. Additionally, the mechanical properties of these alloys indicate a ductile behaviour, which makes them ideal for various engineering and industrial applications. The electronic structures have been meticulously characterized using a quantum mechanical approach. Two spin-polarized approximation schemes have been utilized: the WC generalized gradient approximation (WC-GGA) and the Tran-Blaha modified Becke-Johnson (TB-mBJ). The band structures of Rb 2 ReCl 6 , Rb 2 ReBr 6 , and Rb 2 ReI 6 show semiconducting behaviour, with band gap values of approximately 2.59 eV, 2.2 eV, and 1.55 eV, respectively. The spin magnetic moments for Rb 2 ReCl 6 and Rb 2 ReI 6 were determined to be 3 μB, while Rb 2 ReBr 6 exhibited a slightly lower value of 2.99 μB. The effective mass of holes at the VBM exceeds the effective mass of electrons at the conduction band minimum. Our research reveals that Rb 2 ReCl 6 demonstrates an impressive S coefficient of 1600 μV/K when subjected to hole doping. Based on the observed high Seebeck coefficient and maximum power factor, our study found sig- nificant figures of merit (ZT) for the materials studied: 1.06 for Rb 2 ReCl 6 , 1.07 for Rb 2 ReBr 6 , and 0.98 for Rb 2 ReI 6 . Our findings indicate that Rb 2 ReX 6 compounds, which have a double perovskite structure with X being Chlorine, Bromine or Iodine, show great potential for use in spintronic, photodetectors, and thermoelectric generators (TEGs). This thorough investigation not only enhances our comprehension of these materials but also establishes the foundation for experimentalists to further investigate their potential applications. 1. Introduction With the ongoing rise in global population and economic develop- ment, the demand for energy continues to grow, leading to significant depletion of fossil fuel resources and posing a serious risk to the envi- ronment. Traditional fossil fuels such as oil and coal significantly impact the environment, especially since they release polluting gases into the atmosphere [1,2]. This, in turn, contributes to the concerning issues of global warming and the greenhouse effect. Consequently, there is a pressing need to explore environmentally sustainable and affordable energy sources. Among the various methods for generating electricity, such as hydrothermal and wind power, solar energy is abundant and can be effectively utilized to meet the increasing energy demands. An emerging and promising approach to sustainable energy generation in- volves thermoelectric materials. These materials have the unique ability to directly convert heat into electricity, making them valuable for waste * Corresponding author. E-mail address: mohammed.elgoutni@yahoo.fr (M. El Amine). Contents lists available at ScienceDirect Computational Condensed Matter journal homepage: www.elsevier.com/locate/cocom https://doi.org/10.1016/j.cocom.2025.e01038 Received 27 August 2024; Received in revised form 24 March 2025; Accepted 27 March 2025 Computational Condensed Matter 43 (2025) e01038 Available online 29 March 2025 2352-2143/Published by Elsevier B.V.