Theoretical investigation of the functional and photocatalytic properties of Li2TiX6 (X = Cl, Br, and I) double perovskites using density functional theory

Abstract

This study investigates the untapped potential of Li₂TiX₆ (X = Cl, Br, and I) as high-efficiency photocatalysts using density functional theory (DFT) in the VASP framework. By bridging the gap between structural integrity and electrical behavior, we disclose a family of materials that are both strong and chemically active. Our calculations reveal a diverse bandgap of 1.95 (Cl), 1.29 (Br), and 0.65 eV (I) as obtained using GGA. These bandgap values get widened to 3.29, 2.48 and 1.64 eV, respectively, when using HSE06. An additional SOC calculation was included, which shows that they have small spin–orbit splitting in the band structure with a reduction in bandgap of <0.1 eV for Cl and Br, with I being the most affected compound due to its atomic size. Optical investigation reveals that the compounds have a strong absorption in the UV-visible region, showing a redshift in absorption onset as we transition from Cl → Br → I. In addition to the electronic properties, we performed a thorough mechanical assessment and confirmed the structural endurance of these compounds for long-term device integration by computing the Bulk, Shear, and Young's moduli, as well as Poisson's and Pugh's ratios. Utilizing Mulliken and Pauling electronegativity, we calculate the redox reaction potential, which results in Li₂TiCl₆ having a reduction potential (H⁺/H₂) of −0.107 eV and an oxidation potential (O₂/H₂O) of 3.29 eV, making it the most promising candidate for photocatalytic water splitting among the studied compounds.