Strain-Engineered Magnetism, Super-Exchange Physics, and Thermal Phase Transitions in Monolayer Chromium Trihalides (CrX3, X = Cl, Br, I)

Abstract

This repository contains the simulation dataset, processing scripts, and workflow execution files for the study: "Strain-Engineered Magnetism, Super-Exchange Physics, and Thermal Phase Transitions in Monolayer Chromium Trihalides (CrX3, X = Cl, Br, I)". Abstract:Using a multiscale framework combining Graph Neural Network (CHGNet) interatomic potential relaxations and classical Metropolis Monte Carlo spin simulations, we investigate the impact of in-plane isotropic biaxial strain (ε ∈ [-4%, +4%]) across monolayer CrCl3, CrBr3, and CrI3. Structural optimizations yield 2D elastic stiffness moduli of C2D = 42.1 N/m (CrCl3), 37.8 N/m (CrBr3), and 31.4 N/m (CrI3). Tensile strain monotonically enhances the nearest-neighbor exchange coupling J(ε) across all three materials due to the continuous modification of the Cr-X-Cr super-exchange bond angle towards 90°, translating into a strong linear enhancement of the Monte Carlo Curie temperature Tc(ε). Repository Contents:- 01_chgnet_strain.py: Python script for GNN structural relaxation, 2D elastic modulus C2D fitting, and FM/AFM energy mapping to extract J(ε).- 02_monte_carlo.py: Metropolis Monte Carlo spin dynamics code on 32 × 32 × 1 spin supercells (N = 2,048) for evaluating M(T), χ(T), Binder cumulants U4, and Curie transition temperatures Tc.- 03_build_paper_reportlab.py: Automated report and figure compiler script.- data/strain_results.json: Processed structural parameters, 2D elastic moduli, equilibrium lattice constants a0, and exchange constants J(ε).- data/mc_results.json: Processed thermodynamic ensemble averages, susceptibility peak data, and derived Curie temperatures Tc(ε).- figures/: High-resolution vector figures (PDF/PNG) featured in the main publication.- manuscript.pdf: Complete two-column compiled REVTeX 4.2 manuscript.