Poisson’s ratio in the all-inorganic perovskite monolayers

Poisson’s ratios of two-dimensional (2D) all-inorganic perovskites Cs 2 PbX 4 (X = Cl, Br, I) have been calculated by the first-principles calculations. The contribution of each geometric parameter (bond length [Formula: see text], bond angle [Formula: see text], rotation angle [Formula: see text], and tilt angle [Formula: see text]) to Poisson’s ratio is obtained analytically. Through a comprehensive analysis of the geometric deformations of the perovskite under the uniaxial strain, we find that Poisson’s ratios of the perovskites are sensitive to the change of the bond length [Formula: see text] and the bond angle [Formula: see text]. In addition, the value of the bond angle [Formula: see text] in the strain-free structure mainly determines the high in-plane anisotropy of Poisson’s ratios in Cs 2 PbX 4 .