Search on stable binary and ternary compounds of two-dimensional transition metal halides

Ab initio driven density functional theory (DFT)-based high throughput simulations have been conducted to search for stable two-dimensional (2D) structures based on transition metal halides. Binary MeX2 and MeXY (Me – transition element, X and Y – Cr, Br, I, where X ≠ Y) 2D structures in two structural polymorphic modifications, which are 1T- phase and 1H-phase, have been studied. The main structural stability criteria, such as heat formation energy, elasticity constants, and phonon spectra and the following ab initio molecular dynamics (AIMD) simulations have been used to determine the stability of studied compounds. It has been shown that 35 MeX2 and 32 MeXY 2D structures comply with given stability criteria. Photocatalytic properties of these stable 2D MeX2 and 2D MeXY have been investigated. Based on the calculated band gap size Eg, work function Ф and electron affinity χ, it has been found that among all stable compounds 13 MeX2 and 16 MeXY 2D structures are promising photocatalysts for water splitting. However, only 7 compounds have solar-to-hydrogen (STH) efficiency overcome the 10% threshold, which is a critical parameter for solar hydrogen generation to be an economically viable resource. Among MeX2 2D structures 1T-CdI2 and 1H-VBr2 possess a STH efficiency of 11.58% and 17.23%. In the case of 2D MeXY, STH efficiencies are 22.79% (1T-ZnClI), 15.20% (1T-CdClI), 22.13% (1T-ZnBrI), 12.11% (1T-CdBrI) and 19.76% (1H-VClBr). Moreover, as a result of this work, a comprehensive publicly available database, containing detailed calculation parameters and fundamental properties of the discovered 2D transition metal halides, has been created.