2D planar penta-MN (M = Pd, Pt) sheets identified through structure search.

Two-dimensional (2D) metal dinitrides have attracted increasing attention because of their diverse geometry configurations and extraordinary properties. Using the particle swarm optimization (PSO)-based global structure search method combined with first principles calculations, we have identified 2D metal dinitride MN2 (M = Pd, Pt) sheets containing N2 dimers, penta-MN2, which are planar and composed entirely of pentagons. These pentagonal sheets are not only dynamically, thermally and mechanically stable, but also energetically more favorable over the experimentally synthesized pyrite MN2 monolayers. In particular, penta-PtN2 can withstand a temperature as high as 2000 K, showing its potential as a refractory material. In addition, due to its unique atomic configuration, penta-MN2 exhibits intriguing electronic properties. Penta-PdN2 is metallic, while penta-PtN2 is semiconducting with a direct band gap of 75 meV and an ultrahigh carrier mobility. This study expands the family of 2D metal nitrides, and provides new insight into finding new materials using a reliable structure search algorithm rather than chemical and physical intuition.