Metal halide HgI₂ monolayer with auxetic property and photocatalysis application

Recently, two-dimensional (2D) metal halides have shown extraordinary performances as photocatalysts, triggering our enormous interest to explore new 2D metal halides for photocatalysis water splitting. Here, based on an unbiased first-principles swarm intelligence structure search, we identified a thermally and dynamically stable HgI₂ monolayer. Interestingly, its atomic configuration forms an unusual in-plane negative Poisson's ratio, resulting in an auxetic property. More importantly, the HgI₂ monolayer exhibits excellent optoelectronic properties, including suitable direct bandgap (∼2.45 eV), good carrier mobility (×10² cm² V⁻¹ s⁻¹), excellent light absorption coefficient (×10⁵ cm⁻¹), and suitable band edges for photocatalytic water splitting. These excellent characteristics make the HgI₂ monolayer fulfill the basic criteria of efficient photocatalysts for water splitting, supporting it as a promising candidate for photocatalytic materials. Our findings bloom the 2D metal halides family and offer a new candidate material for photocatalysis water splitting.