Many-body benchmarking of density functional theory local-registry energetics in bilayer InSe
Phys. Rev. B 114, 225421 – Published 28 October, 2026
DOI: https://doi.org/10.1103/1mnm-51c5
Abstract
Density functional theory (DFT) is widely used to model twisted bilayers, but the accuracy of the local stacking energetics underlying such models remains uncertain. Here, we benchmark the local-registry landscape of bilayer InSe using diffusion quantum Monte Carlo (DMC). DFT predicts that AB, AAr, and ABr stackings, which share the same interfacial Se registry, are nearly degenerate within 1.5 meV/f.u. DMC instead separates these stackings by 8(5) and 41(4) meV/f.u., while the energy difference between the most stable and least stable registries reaches 60(7) meV/f.u. The corresponding DMC density redistribution is also strongly registry-dependent, whereas the vdW-DF and rev-vdW-DF2 density responses examined here remain much more similar among these stackings. These large energy separations show that the stacking energetics are not determined by the interfacial atomic motif alone but depend on the full registry and its associated many-body electronic response. For bilayer InSe, the tested DFT approximations substantially underestimate the local stacking-energy corrugation, highlighting the need to validate the local-registry energy scale used in moiré modeling because errors in this scale can propagate into predictions of structural relaxation, domain formation, and electronic reconstruction.
