2D planar penta-MN2 (M = Pd, Pt) sheets identified through structure search

Abstract

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.