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REVIEW 2 major objections 1 minor 29 references

First-principles calculations find pronounced spin splitting near the band edges in both (R/S-PEA)PbI₃ and (R/S-NEA)PbI₃, with stronger effective valence-band splitting in the NEA compounds.

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2026-07-02 09:37 UTC pith:TYNT4KQV

load-bearing objection The calculations show a clear difference in effective valence-band spin splitting between the PEA and NEA compounds driven by multiband effects, but the result sits on untested DFT choices. the 2 major comments →

arxiv 2607.00933 v1 pith:TYNT4KQV submitted 2026-07-01 cond-mat.mtrl-sci

First-principles calculations of spin-split bands in chiral hybrid organic-inorganic perovskites (R/S-PEA)PbI₃ and (R/S-NEA)PbI₃

Tetsuya Furukawa , Kazushi Nakano , Youta Suzuki , Takumi Kaneko , Ayumi Ishii , Tetsuaki Itou This is my paper
classification cond-mat.mtrl-sci
keywords chiral hybrid perovskitesspin splittingspin-orbit couplingfirst-principles calculationsband structureorganic-inorganic perovskitesnonsymmorphic space group
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

The paper carries out density-functional-theory calculations that include spin-orbit coupling to determine the electronic band structures of two one-dimensional chiral hybrid perovskites. It reports clear spin splitting at both the valence-band maximum and conduction-band minimum in each material. The effective size of the splitting at the valence-band edge turns out larger for the NEA-based compounds than for the PEA-based ones, even though the linear-in-k coefficients near high-symmetry points are comparable. The difference is traced to larger spin-orbit-induced gaps and the pattern of band crossings or avoided crossings that appear in the multiband structure of the NEA material. The same calculations also show that, for a fixed molecular handedness, the two compounds produce opposite spin textures, in line with their opposite chiral distortions of the inorganic octahedra.

Core claim

Both compounds exhibit pronounced spin splitting near the valence-band maximum and conduction-band minimum. The effective spin splitting of the edges of the valence bands is stronger in (R/S-NEA)PbI₃ despite similar linear-in-k splitting coefficients near the relevant high-symmetry points. This enhancement originates from larger gaps induced by spin-orbit coupling at high-symmetry points and band (anti)crossings in the multiband structure. For a given molecular handedness, the PEA- and NEA-based compounds exhibit opposite spin textures, consistent with the opposite chiral distortions of the [PbI₆]⁴⁻ octahedra.

What carries the argument

Density-functional-theory band-structure calculations that include spin-orbit coupling, combined with orbital projections showing Pb versus molecular-orbital character and group-theoretical analysis of the nonsymmorphic space group P2₁2₁2₁ that explains band sticking and symmetry-enforced degeneracies.

Load-bearing premise

The chosen exchange-correlation functional, pseudopotentials, and structural-relaxation protocol produce spin-split bands whose quantitative features are not dominated by standard density-functional-theory approximations for heavy-element systems with strong spin-orbit coupling.

What would settle it

Spin-resolved photoemission or circular-dichroism measurements that either confirm or contradict the predicted opposite spin textures for PEA- and NEA-based compounds of the same molecular handedness.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

  • The larger effective valence-band splitting in NEA compounds follows directly from the bigger spin-orbit gaps and the multiband crossings present in that structure.
  • Opposite spin textures for the same handedness are required by the opposite sense of octahedral distortion in the two families.
  • Group theory for the P2₁2₁2₁ space group accounts for the locations where spin polarization must vanish at zone-boundary points.
  • The orbital character of the conduction bands differs: Pb-dominated in PEA compounds, hybridized with the NEA lowest unoccupied molecular orbital in NEA compounds.

Where Pith is reading between the lines

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

  • Choosing different organic cations could provide a route to engineer the magnitude of spin splitting while preserving the same space group and handedness.
  • The connection between octahedral distortion direction and spin-texture sign offers a concrete handle for designing materials with targeted electromagnetic responses.
  • The band-crossing mechanism identified here could be tested by varying the strength of spin-orbit coupling through chemical substitution of the inorganic ions.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

2 major / 1 minor

Summary. The manuscript reports first-principles DFT+SOC calculations on the one-dimensional chiral hybrid perovskites (R/S-PEA)PbI₃ and (R/S-NEA)PbI₃. It finds pronounced spin splitting near the valence-band maximum and conduction-band minimum in both compounds, with stronger effective spin splitting of the valence-band edges in the NEA-based material despite comparable linear-in-k coefficients near high-symmetry points; this difference is attributed to larger SOC-induced gaps and band (anti)crossings in the multiband structure. For a given molecular handedness the two compounds show opposite spin textures, consistent with opposite chiral distortions of the [PbI₆]⁴⁻ octahedra. Group-theoretical analysis of the nonsymmorphic P2₁2₁2₁ space group is used to explain band sticking, symmetry-enforced degeneracies, and vanishing spin polarization at certain zone-boundary points.

Significance. If the reported quantitative differences prove robust, the work supplies a direct comparison of how molecular size and resulting octahedral distortions modulate chirality-induced spin splitting, together with symmetry-based explanations for the observed spin textures. This provides a concrete foundation for interpreting circular-dichroism and related electromagnetic responses in chiral HOIPs. The calculations are direct outputs of electronic-structure methods with no fitted parameters or circular definitions.

major comments (2)
  1. [Computational Methods] Computational Methods (or equivalent section describing the DFT setup): No convergence tests with respect to k-mesh density, plane-wave cutoff energy, or smearing are reported, nor is the exchange-correlation functional (PBE or hybrid) or the protocol for structural relaxation (with or without SOC) specified. In heavy-element systems with strong SOC these choices are known to affect both the magnitude and, in some cases, the sign of spin splittings; without such controls the central claim that the effective valence-band splitting is stronger in (R/S-NEA)PbI₃ than in (R/S-PEA)PbI₃ cannot be considered secured.
  2. [Results] Results section discussing effective spin splitting and band crossings: The attribution of the NEA enhancement to larger SOC gaps and multiband (anti)crossings is presented as the origin of the difference, yet no quantitative error bars, comparison to hybrid-functional results, or benchmark against available experimental spin-splitting data are supplied. This leaves open the possibility that the reported difference is dominated by the semi-local functional approximation rather than by the structural and multiband features emphasized in the text.
minor comments (1)
  1. [Abstract] The abstract states that calculations were performed but does not name the functional or basis-set details; adding one sentence on the computational protocol would improve readability for readers interested in reproducibility.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments, which help improve the clarity and robustness of our manuscript. We address each major comment below.

read point-by-point responses

  1. Referee: [Computational Methods] Computational Methods (or equivalent section describing the DFT setup): No convergence tests with respect to k-mesh density, plane-wave cutoff energy, or smearing are reported, nor is the exchange-correlation functional (PBE or hybrid) or the protocol for structural relaxation (with or without SOC) specified. In heavy-element systems with strong SOC these choices are known to affect both the magnitude and, in some cases, the sign of spin splittings; without such controls the central claim that the effective valence-band splitting is stronger in (R/S-NEA)PbI₃ than in (R/S-PEA)PbI₃ cannot be considered secured.

    Authors: We agree that the Computational Methods section must be expanded for reproducibility. In the revised manuscript we will explicitly state the exchange-correlation functional (PBE), k-mesh density, plane-wave cutoff, smearing parameters, and relaxation protocol (structural optimization without SOC followed by SOC calculations). We will also add convergence tests confirming that the reported spin splittings are stable with respect to these settings. These additions will directly support the reliability of the NEA versus PEA comparison. revision: yes

  2. Referee: [Results] Results section discussing effective spin splitting and band crossings: The attribution of the NEA enhancement to larger SOC gaps and multiband (anti)crossings is presented as the origin of the difference, yet no quantitative error bars, comparison to hybrid-functional results, or benchmark against available experimental spin-splitting data are supplied. This leaves open the possibility that the reported difference is dominated by the semi-local functional approximation rather than by the structural and multiband features emphasized in the text.

    Authors: We acknowledge the absence of hybrid-functional results and experimental benchmarks. While PBE+SOC is standard for these systems and the differences are linked to the distinct octahedral distortions and band crossings (computed consistently for both compounds), we agree that additional context is warranted. In revision we will add a limitations paragraph discussing the expected accuracy of PBE for spin splittings in lead halides, provide parameter-based error estimates, and note the current lack of direct experimental spin-splitting data for these 1D chiral perovskites. Hybrid calculations for the large unit cells remain computationally intensive and will not be added at this stage. revision: partial

Circularity Check

0 steps flagged

No circularity: spin splittings are direct outputs of DFT+SOC calculations

full rationale

The paper reports results from standard first-principles DFT calculations (including SOC) on the two specific compounds. The central claims concern computed band structures, spin splittings near VBM/CBM, differences between PEA and NEA compounds, and their attribution to SOC gaps and band crossings. These quantities are numerical outputs of the electronic-structure solver applied to the relaxed geometries and chosen functional/pseudopotentials; they are not defined in terms of themselves, fitted from the target data, or reduced via self-citation chains. No equations, ansatzes, or uniqueness theorems are invoked that would make the reported effective splittings or textures tautological with the inputs. The group-theoretical analysis for P2_12_12_1 is an independent symmetry classification applied after the bands are obtained. Self-citations, if present, are not load-bearing for the quantitative differences. This is the normal non-circular case for a direct computational study.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the validity of standard DFT+SOC for these systems; no free parameters are explicitly fitted to the target spin-splitting quantities in the abstract, and no new entities are postulated.

axioms (1)
  • domain assumption Density-functional theory with spin-orbit coupling, using standard approximations, yields spin-split bands whose relative strengths between the two compounds are physically meaningful.
    The paper states that first-principles calculations including SOC were performed and directly compares the resulting band features.

pith-pipeline@v0.9.1-grok · 5939 in / 1493 out tokens · 31334 ms · 2026-07-02T09:37:39.330917+00:00 · methodology

0 comments
read the original abstract

Chiral hybrid organic-inorganic perovskites provide a promising platform for investigating the physics of chirality-driven spin-split bands because they combine robust molecular chirality with strong spin-orbit coupling from heavy inorganic ions. First-principles calculations including spin-orbit coupling are performed for the one-dimensional chiral perovskites ($R$/$S$-PEA)PbI$_3$ and ($R$/$S$-NEA)PbI$_3$ to compare their spin-split band structures and to identify the factors controlling their differences. In ($R$/$S$-PEA)PbI$_3$, the lowest conduction bands predominantly consist of Pb orbitals, whereas in ($R$/$S$-NEA)PbI$_3$, they are formed by hybridization between Pb orbitals and the lowest unoccupied molecular orbital of NEA. Both compounds exhibit pronounced spin splitting near the valence-band maximum and conduction-band minimum. The effective spin splitting of the edges of the valence bands is stronger in ($R$/$S$-NEA)PbI$_3$, despite similar linear-in-$k$ splitting coefficients near the relevant high-symmetry points. This enhancement originates from larger gaps induced by spin-orbit coupling at high-symmetry points and band (anti)crossings in the multiband structure. For a given molecular handedness, the PEA- and NEA-based compounds exhibit opposite spin textures, consistent with the opposite chiral distortions of the [PbI$_6$]$^{4-}$ octahedra and with the previously observed opposite signs of circular dichroism. Group-theoretical analysis for the nonsymmorphic space group $P2_12_12_1$ further accounts for band sticking, symmetry-enforced degeneracies, and the disappearance of spin polarization at specific Brillouin-zone-boundary points. These results provide a solid foundation for future studies of chirality-dependent electromagnetic responses, including circular dichroism, in chiral hybrid organic-inorganic perovskites.

Figures

Figures reproduced from arXiv: 2607.00933 by Ayumi Ishii, Kazushi Nakano, Takumi Kaneko, Tetsuaki Itou, Tetsuya Furukawa, Youta Suzuki.

Figure 1
Figure 1. Figure 1: FIG. 1. Crystal structures of ( [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Electronic structures of ( [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Spin-split band dispersions of ( [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Schematic spin-split band dispersions of the lowest [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. Spin-split band dispersions of ( [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗
Figure 7
Figure 7. Figure 7: FIG. 7. Energy splitting magnitude [PITH_FULL_IMAGE:figures/full_fig_p007_7.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6. Enlarged views of the spin-split bands of ( [PITH_FULL_IMAGE:figures/full_fig_p007_6.png] view at source ↗
Figure 8
Figure 8. Figure 8: FIG. 8. Schematic band dispersions showing the enhance [PITH_FULL_IMAGE:figures/full_fig_p008_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: FIG. 9. Character tables of the space group [PITH_FULL_IMAGE:figures/full_fig_p009_9.png] view at source ↗

discussion (0)

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Reference graph

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