High-throughput computational screening of auxetic two-dimensional metal dichalcogenides and dihalides

Auxetic materials hold tremendous potential for many advanced applications, but candidates are quite scarce, especially at two dimensions. Here, we focus on two-dimensional (2D) metal dichalcogenides and dihalides with the chemical formula MX₂ by screening structures sharing the P 4 ̄ m2 space group among 330 MX₂ compounds from the computational 2D materials database. Via high-throughput first-principles computations, 25 stable MX₂ (M = Mg, Ca, Mn, Co, Ni, Cu, Zn, Ge, Cd, Sn; X = F, Cl, Br, I, O, S, Se) systems with in-plane negative Poisson’s ratios (NPRs) are successfully identified. Within these structures, 2D NiCl₂ has the largest NPR value of −0.34, with a magnitude significantly higher than those of black phosphorene (−0.027) and SnO₂ (−0.1). The distinct auxetic effect in MX₂ originates from both the unique local corner-sharing tetrahedral structural motif under the low-dimensional effect and the strong orbital interaction between the d orbitals of M and the p orbitals of halogen/chalcogen atoms. As a result, Poisson’s ratio can be effectively tuned by enhancing the d-p interaction through an external biaxial strain. We reveal that these auxetic materials exhibit rich electronic and magnetic properties, covering nonmagnetic, ferromagnetic, or anti-ferromagnetic metals, semiconductors, and insulators. The extraordinary auxetic behaviors in combination with rich physical properties could lead to multifunctional nanomechanical, optoelectronic, and spintronic applications.