Metal halide HgI 2 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 HgI 2 monolayer. Interestingly, its atomic configuration forms an unusual in-plane negative Poisson's ratio, resulting in an auxetic property. More importantly, the HgI 2 monolayer exhibits excellent optoelectronic properties, including suitable direct bandgap (∼2.45 eV), good carrier mobility (×10 2 cm 2 V −1 s −1 ), excellent light absorption coefficient (×10 5 cm −1 ), and suitable band edges for photocatalytic water splitting. These excellent characteristics make the HgI 2 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.