High-Throughput Discovery and Investigation of Auxetic Two-Dimensional Crystals

Auxetic two-dimensional (2D) crystals that yield a negative Poisson’s ratio (NPR) exhibit unusual transverse expansion when stretched. Such materials have great potential for electronic skins, energy harvesting, mechatronic shape display devices, and strain sensors. However, most 2D crystals have positive Poisson’s ratios, and the number of existing 2D materials with NPR is limited. Accelerating the discovery of these rare auxetic materials remains a long-term challenge. Utilizing high-throughput computations, this work discovers 108 stable 2D crystals with negative in-plane Poisson’s ratios that could be successfully fabricated from the 4047 2D crystals in the Computational 2D Materials Database (C2DB). We find 4 crystal types with the potential for significant auxetic effect regardless of the orientations, that is, MX2O8, MX2O6, MX3, and MXX′. The auxetic effects for the former two are simply from crystal geometry, while further first-principles calculations based on MX3 (M = Sc, Ti, V, Cr, ... and X = Cl, Br, I) and MXX′ (M = Mn, Fe, Co, Ni; X = Li, Na, Mg, Ca, Sr; and X′ = Si, Ge, P, As, Sb) reveal that the NPR originates from both the crystal geometry and electronic structures. Because some databases lack the information of elasticity and stability, deep learning models are trained using C2DB and employed to find 92 other stable 2D crystals with NPR. The band gaps of the 200 stable auxetic 2D crystals discovered in our work cover a wide range from 0 to 5.7 eV, which provide abundant candidates for nanoscale electronics with intriguing physicochemical properties.