High-Throughput Discovery and Investigation of Auxetic TwoDimensional Crystals br

Auxetic two-dimensional (2D) crystals that yield anegative Poisson's ratio (NPR) exhibit unusual transverse expansionwhen stretched. Such materials have great potential for electronicskins, energy harvesting, mechatronic shape display devices, andstrain sensors. However, most 2D crystals have positive Poisson'sratios, and the number of existing 2D materials with NPR is limited.Accelerating the discovery of these rare auxetic materials remains along-term challenge. Utilizing high-throughput computations, thiswork discovers 108 stable 2D crystals with negative in-planePoisson's ratios that could be successfully fabricated from the 40472D crystals in the Computational 2D Materials Database (C2DB).Wefind 4 crystal types with the potential for significant auxetic effectregardless of the orientations, that is, MX2O8,MX2O6,MX3, andMXX '. The auxetic effects for the former two are simply from crystalgeometry, while furtherfirst-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 andelectronic structures. Because some databases lack the information of elasticity and stability, deep learning models are trained usingC2DB and employed tofind 92 other stable 2D crystals with NPR. The band gaps of the 200 stable auxetic 2D crystals discovered inour work cover a wide range from 0 to 5.7 eV, which provide abundant candidates for nanoscale electronics with intriguingphysicochemical properties