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arxiv: 2607.01682 · v1 · pith:MYKQ7CX3new · submitted 2026-07-02 · ❄️ cond-mat.mtrl-sci

Many-body benchmarking of DFT local-registry energetics in bilayer InSe

Jeonghwan Ahn , Abdulgani Annaberdiyev , Jovan Nelson , Nathaniel P. Stern , Hyeondeok Shin This is my paper

Pith reviewed 2026-07-03 10:19 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci
keywords bilayer InSestacking energeticsdiffusion Monte CarloDFT benchmarkingtwisted bilayersmany-body effectsmoiré potentialsvan der Waals materials
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The pith

DMC shows InSe bilayer stackings differ by up to 60 meV per formula unit while DFT finds them nearly degenerate.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper benchmarks local registry energies in bilayer InSe by comparing diffusion quantum Monte Carlo results against density functional theory. DMC finds that three stackings sharing the same interfacial Se atoms are separated by 8 and 41 meV per formula unit, with the full range reaching 60 meV, whereas DFT keeps them within 1.5 meV. The separation demonstrates that registry energy is set by the complete atomic arrangement and its many-body electronic response, not by the interface motif alone. This directly affects how accurately DFT-based moiré models can describe relaxation, domains, and electronic structure in twisted bilayers.

Core claim

DMC separates AB, AAr, and ABr 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.. 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. More broadly, these results show that DFT-based moiré models can substantially underestimate local stacking-energy corrugation, with direct consequences for predicted structural relaxation, domain formation, and electronic reconstruction in twisted layered materials.

What carries the argument

Diffusion quantum Monte Carlo (DMC) applied to the three high-symmetry stackings of bilayer InSe to extract registry-dependent total energies beyond DFT.

If this is right

  • Twisted InSe bilayers will exhibit stronger structural relaxation and larger domain sizes than DFT moiré models predict.
  • Electronic reconstruction at domain walls will be more pronounced because of the deeper local energy wells.
  • Similar underestimation of stacking corrugation is expected in other van der Waals bilayers when only DFT is used.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Models that fit moiré potentials from DFT alone may need systematic corrections derived from many-body methods for quantitative predictions of twist-angle-dependent properties.
  • Local stacking energies could be measured by combining atomic-resolution imaging with spectroscopy to test the DMC scale directly.
  • The many-body contribution may also affect phonon modes or excitonic binding that depend on interlayer registry.

Load-bearing premise

The three chosen high-symmetry stackings represent the dominant local registries that appear in a continuously twisted bilayer and that the DMC energies for these discrete cells capture the main many-body contributions without large finite-size or convergence errors.

What would settle it

A converged DMC or higher-level calculation on larger supercells that brings the registry energy spread below roughly 10 meV per formula unit, or an experimental probe that measures stacking-energy differences near the DFT values, would falsify the central claim.

Figures

Figures reproduced from arXiv: 2607.01682 by Abdulgani Annaberdiyev, Hyeondeok Shin, Jeonghwan Ahn, Jovan Nelson, Nathaniel P. Stern.

Figure 1
Figure 1. Figure 1: FIG. 1. High-symmetry bilayer InSe registries and DFT benchmark quantities. (a) Atomic struc [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. DFT sliding landscapes of bilayer InSe. Stacking-dependent energy maps ((a) and (d)), [PITH_FULL_IMAGE:figures/full_fig_p006_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. DMC binding-energy curves for the five bilayer InSe stackings. Dotted lines show Morse [PITH_FULL_IMAGE:figures/full_fig_p009_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Registry-dependent charge redistribution upon bilayer formation, defined as [PITH_FULL_IMAGE:figures/full_fig_p012_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. Twist-angle dependence from DFT and comparison with the DMC local-registry bench [PITH_FULL_IMAGE:figures/full_fig_p014_5.png] view at source ↗
read the original 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. and exhibit nearly indistinguishable DFT charge-density responses. 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.. 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. More broadly, these results show that DFT-based moir\'e models can substantially underestimate local stacking-energy corrugation, with direct consequences for predicted structural relaxation, domain formation, and electronic reconstruction in twisted layered materials.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 0 minor

Summary. The paper claims that DFT finds AB, AAr, and ABr stackings in bilayer InSe nearly degenerate (within 1.5 meV/f.u.) with similar charge densities, while DMC calculations separate them by 8(5) and 41(4) meV/f.u. with a maximum range of 60(7) meV/f.u.; this demonstrates that local stacking energetics depend on the full registry and many-body electronic response rather than the shared interfacial Se motif alone, implying that DFT-based moiré models substantially underestimate corrugation and its consequences for relaxation and reconstruction.

Significance. If the DMC energy differences hold after addressing statistical and convergence issues, the result provides a valuable many-body benchmark for twisted bilayer energetics in InSe, highlighting limitations of DFT local-registry approximations with direct implications for moiré modeling in layered materials. The direct DMC vs. DFT comparison on identical configurations is a strength.

major comments (2)
  1. [Abstract] Abstract and results: The reported DMC energy difference of 8(5) meV/f.u. between AB and AAr stackings is only ~1.6σ from zero. This marginal separation undermines the central claim that DMC 'separates these stackings' and that energetics 'are not determined by the interfacial atomic motif alone,' since the headline assertion requires all three registries to be distinctly resolved beyond the DFT near-degeneracy.
  2. [Methods] Methods/results: No convergence tests, system-size scaling, or detailed methodology (e.g., twist-angle handling, finite-size corrections, or DMC parameters) are provided for the InSe bilayer. This directly threatens verification of the many-body response conclusion and the weakest assumption that the discrete high-symmetry configurations capture the dominant effects without specific convergence errors.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript and for highlighting these important points regarding statistical significance and methodological details. We respond to each major comment below.

read point-by-point responses

  1. Referee: [Abstract] Abstract and results: The reported DMC energy difference of 8(5) meV/f.u. between AB and AAr stackings is only ~1.6σ from zero. This marginal separation undermines the central claim that DMC 'separates these stackings' and that energetics 'are not determined by the interfacial atomic motif alone,' since the headline assertion requires all three registries to be distinctly resolved beyond the DFT near-degeneracy.

    Authors: We agree that the 8(5) meV/f.u. difference is only ~1.6σ and is therefore marginal, which weakens the assertion of clear separation specifically between AB and AAr. The larger 41(4) meV/f.u. separation and 60(7) meV/f.u. overall range still demonstrate that the three stackings are not all near-degenerate within the DFT value of 1.5 meV/f.u., supporting the broader conclusion that energetics depend on the full registry. We will revise the abstract and main text to qualify the AB-AAr result explicitly in terms of its statistical significance while retaining the claim for the resolved separations. revision: partial

  2. Referee: [Methods] Methods/results: No convergence tests, system-size scaling, or detailed methodology (e.g., twist-angle handling, finite-size corrections, or DMC parameters) are provided for the InSe bilayer. This directly threatens verification of the many-body response conclusion and the weakest assumption that the discrete high-symmetry configurations capture the dominant effects without specific convergence errors.

    Authors: The submitted manuscript indeed omits explicit convergence tests, system-size scaling, finite-size corrections, and full DMC parameter details. We will add these in a revised methods section, including justification that the high-symmetry commensurate configurations are appropriate for isolating local-registry effects. Since the study addresses fixed bilayer stackings rather than incommensurate twisted structures, twist-angle handling does not apply and will be clarified as such. revision: yes

Circularity Check

0 steps flagged

No circularity: energies are direct outputs of independent DMC/DFT runs on fixed configurations.

full rationale

The paper computes total energies for three high-symmetry stackings via DMC and DFT on explicitly defined atomic geometries. The reported differences (8(5), 41(4), 60(7) meV/f.u.) are numerical results of those runs, not quantities obtained by fitting a parameter to a subset of the same data, by algebraic reduction to an input, or by a self-citation chain that itself depends on the target result. No equations or ansätze are introduced that would make any claimed separation equivalent to its own inputs by construction. The central claim therefore rests on external, falsifiable simulation outputs rather than on any of the enumerated circularity patterns.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Only the abstract is available, so the ledger reflects typical background assumptions for DFT/DMC calculations on 2D materials; no ad-hoc parameters or new entities are mentioned.

axioms (1)
  • standard math Born-Oppenheimer approximation and standard pseudopotential treatment of core electrons are valid for the InSe bilayer.
    These are implicit background assumptions in all DFT and DMC calculations of this type.

pith-pipeline@v0.9.1-grok · 5740 in / 1340 out tokens · 49063 ms · 2026-07-03T10:19:24.454607+00:00 · methodology

discussion (0)

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Reference graph

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