Electronic structure and magnetism in MnBi₂Te₄: a diffusion Monte Carlo and DFT Study

The layered vdW MnBi₂Te₄ (MBT) material has attracted substantial attention recently due to claims that it is the first observed Z2 AFM topological insulator. Experimental measurements show that MBT has A-type AFM magnetic structure with intralayer FM order and interlayer AFM order. Some magnetic and electronic properties, however, remain unclear, for instance, measured local magnetic moments on the Mn site are widely scattered (4-6 μ_B) and calculated DFT band gaps are sensitive to model parameters and therefore require tuning to experiment. In this work, we use the benchmarking fixed-node diffusion Monte Carlo (FNDMC) method to shed light on these properties. By integrating angular averages of the FNDMC spin-densities at the Mn sites with optimized nodes, we provide predictive insights into the local moment. Additionally, we exploit the variational property of FNDMC to parameterize DFT models that require no experimental inputs to estimate an ab initio band gap that agrees with measured values for this topological material.