Comprehensive Investigation of Physical Properties of <i> Cs ₂ VX ₆ </i> ( <i>X</i> = Cl, I, or Br) Vacancy‐Ordered Double Perovskites

ABSTRACT In the quest for next‐generation technology, spintronics and optoelectronics have emerged as pivotal fields for developing energy‐efficient and high‐speed devices. Vacancy‐ordered double perovskites are promising candidates for these applications due to the tunability of their band gaps, their robust spin polarization at the Fermi level, and their environmental stability. This research presents a comprehensive ab initio investigation of the quaternary Cs 2 VCl 6 , Cs 2 Vl 6 , and Cs 2 VBr 6 compounds, leveraging an all‐electron Density Functional Theory (DFT) approach, implemented through the high‐precision Full‐Potential Linearized Augmented Plane‐Wave (FP‐LAPW) formalism, as embodied within the WIEN2k computational suite. To ensure high accuracy, the TB‐mBJ potential was utilized for electronic and optical excitations. Structural relaxation verified that all studied configurations reside in a global energy minimum, ensuring both the mechanical robustness and dynamical stability of the cubic phase. Electronic and magnetic analyses revealed that these vacancy‐ordered double perovskites exhibit a robust half‐metallic ferromagnetic ground state with a fully quantized total magnetic moment of 1.00 . Specifically, they display minority‐channel spin‐flip gaps of 2.94, 2.36, and 1.45 eV for Cs 2 Vcl 6 , Cs 2 VBr 6 , and Cs 2 Vl 6 , respectively. Furthermore, optical calculations demonstrated exceptionally high absorption coefficients (reaching the range) in the ultraviolet‐visible spectrum. Thermoelectric analysis yielded outstanding peak Figure of Merit (ZT) values of 0.69 for C s 2 VCl 6 , 0.95 for Cs 2 VBr 6 , and 1.96 for Cs 2 Vl 6 at high temperature. Consequently, these quantitative findings strongly demonstrate that C s 2 VCl 6 , Cs 2 Vl 6 , and Cs 2 VBr 6 possess tremendous potential for next‐generation spintronic, optoelectronic, and thermoelectric device integration.