Enabling Intrinsic Antiferroelectricity in Two-dimensional NbOCl₂: Molecular Dynamics Simulations based on Deep Learning Interatomic Potential

Compared to the well-studied two-dimensional (2D) ferroelectricity, the appearance of 2D antiferroelectricity is much rarer, where local dipoles from the nonequivalent sublattices within 2D monolayers are oppositely oriented. Using NbOCl₂ monolayer with competing ferroelectric (FE) and antiferroelectric (AFE) phases as a 2D material platform, we demonstrate the emergence of intrinsic antiferroelectricity in NbOCl₂ monolayer under experimentally accessible shear strain, along with new functionality associated with electric field-induced AFE-to-FE phase transition. Specifically, the complex configuration space accommodating FE and AFE phases, polarization switching kinetics, and finite temperature thermodynamic properties of 2D NbOCl₂ are all accurately predicted by large-scale molecular dynamics simulations based on deep learning interatomic potential model. Moreover, room temperature stable antiferroelectricity with low polarization switching barrier and one-dimensional collinear polarization arrangement is predicted in shear-deformed NbOCl₂ monolayer. The transition from AFE to FE phase in 2D NbOCl₂ can be triggered by a low critical electric field, leading to a double polarization–electric (P–E) loop with small hysteresis. A new type of optoelectronic device composed of AFE-NbOCl₂ is proposed, enabling electric “writing” and nonlinear optical “reading” logical operation with fast operation speed and low power consumption.