{"id":"b97d41ec-00d6-4026-98a0-fa914086840f","arxiv_id":"2607.27554","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Two new metastable BN monolayers, pentaoctite-BN and pop-BN, are predicted to be dynamically, mechanically, and thermally stable indirect-gap semiconductors with strong excitonic absorption tunable from visible to telecom infrared.","lead":"Using quantum-mechanical computer simulations, the authors predict two new flat boron-nitride sheets with pentagon–octagon rings that should be stable as metastable semiconductors. The interest is that rearranging the atomic lattice alone could shift boron nitride's optical response from ultraviolet to visible and infrared wavelengths without changing its chemistry.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 'viable 2D material' claim rests on a 10 ps, 300 K AIMD run with no barrier calculation; kinetic stability to h-BN conversion is unverified.","rationale":"The reader's weakest-assumption analysis identifies the same load-bearing concern: the leap from short, single-temperature AIMD and local stability criteria to the conclusion of viability. I reviewed the rest of the manuscript for internal errors—the electronic structure, elastic constants, phonon dispersion, and optical calculations are internally consistent and follow standard methods for this class of 2D materials. No mathematical or logical error jumps out. The missing barrier calculation is the most serious gap because the entire 'viable material' conclusion depends on kinetic stability, and the thermodynamic driving force toward h-BN is large. A 10 ps trajectory at 300 K is insufficient to observe a rare transformation event, especially if the barrier is low but not negligible. The proposed NEB calculation would directly measure the barrier and settle the concern. Since the reader already conditioned the verdict on this issue, my read does not change the verdict; it remains CONDITIONAL until the kinetic stability is quantified.","tokens_in":11887,"tokens_out":7722,"duration_ms":87777,"concrete_test":"Perform climbing-image nudged elastic band (CI-NEB) or solid-state NEB calculations connecting PO-BN and PP-BN to h-BN (or to a known lower-energy reconstruction) using a supercell large enough to accommodate the lattice mismatch. Estimate the minimum barrier per atom. If the barrier is below ~0.5 eV/atom (or below k_B times the synthesis temperature), the 'viable' claim fails; if it is above ~1 eV/atom, the claim is supported. Complement with AIMD at 500 K and 1000 K for at least 20 ps to see whether the pentagon–octagon network reconstructs. The barrier is the decisive quantity because it directly tests kinetic stability, which the 10 ps run cannot.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim that PO-BN and PP-BN are viable 2D materials requires kinetic stability, but the paper establishes only local stability: no imaginary phonons (Sec. 3.4), Born–Huang criteria (Sec. 3.3), and a 10 ps NVT AIMD at a single temperature of 300 K (Sec. 3.1). A 10 ps trajectory cannot exclude a low-barrier transformation to h-BN; the transition rate is exponentially sensitive to the barrier, and a barrier of a few tenths of an eV would leave the phase intact for nanoseconds but not for seconds or longer. The authors report ΔE = 644–762 meV/atom relative to h-BN but do not compute any minimum-energy path or activation barrier, nor do they run AIMD at elevated temperatures or for longer times. In Sec. 3.1 they write that a positive ΔE does not rule out realization 'provided that the phase is dynamically, thermally, and mechanically stable'—this is the load-bearing assumption, and it is asserted rather than demonstrated. Without a barrier height or free-energy estimate, the abstract's 'viable two-dimensional materials' and the conclusions' 'thermally stable' overreach the evidence.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript proposes two non-hexagonal boron nitride monolayers, PO-BN and PP-BN, and reports a first-principles characterization of their structural, electronic, elastic, vibrational, thermal, and optical properties. The authors find both phases to be metastable relative to h-BN by 644 and 762 meV/atom, respectively, yet stable against small deformations: positive elastic constants satisfying Born–Huang criteria, no imaginary phonon modes, and preservation of the lattice during a 10 ps AIMD run at 300 K. Both are indirect-gap semiconductors with HSE06 gaps of 3.26 and 2.59 eV, dominated by pz states at the band edges. BSE calculations with a scissor correction place the first bright excitonic absorption at 1.588/1.712 eV for PO-BN and 0.684/0.816 eV for PP-BN, leading the authors to conclude that lattice engineering can tune BN optical response from the ultraviolet to the telecom infrared.","tokens_in":12194,"tokens_out":2771,"duration_ms":34922,"significance":"If the predictions hold, the paper would extend the known 2D BN family beyond the honeycomb lattice, providing concrete metastable polymorphs with a clear structural motif (5–8 rings) and widely tunable optical gaps. The work is genuinely useful as a systematic first-principles survey: the authors connect the pentagon–octagon topology to elastic anisotropy, phonon mode character, and band-edge orbital composition, and they benchmark energetic costs against other metastable 2D lattices. The presentation is generally clear, and the qualitative physical picture is internally consistent. However, the central 'viable 2D material' claim rests on a narrow set of stability tests, and several quantitative results lack convergence evidence; these gaps currently place the paper in the 'defensible, not strongly verified' category rather than at the level needed for a definitive claim of experimental viability.","major_comments":[{"comment":"The thermal-stability evidence consists solely of a 10 ps NVT AIMD run at 300 K (Fig. 3). Given the large metastability energies (644–762 meV/atom), the phrase 'viable two-dimensional materials' and 'thermally stable' require a kinetic argument: a low barrier to reconstruction into h-BN could leave the phase intact for tens of picoseconds but make it unobservable on experimental timescales. The paper provides no minimum-energy path, no climbing-image NEB barrier, and no elevated-temperature AIMD. I ask the authors either to (i) compute an estimate of the barrier separating each phase from h-BN or from likely reconstruction products, (ii) run longer/higher-T simulations that begin to bracket the barrier, or (iii) explicitly tone down the viability claim to 'locally stable on the 10 ps AIMD timescale and dynamically/mechanically stable,' which is all the current evidence supports.","section":"Sec. 3.1 (Thermal stability) and Conclusions"},{"comment":"No convergence tests are reported for any of the key numerical parameters: plane-wave cutoff (550 eV), k-point mesh (7×10×1 and 7×5×1), phonon supercell size (4×4×1), or the BSE basis (9 occupied/9 unoccupied bands, 90 eV response cutoff). Because the paper reports quantitative values for elastic constants, phonon frequencies, HSE06 gaps, and exciton energies to four significant figures, the absence of convergence checks makes the precision hard to evaluate. At minimum, please provide a convergence table for total energy, band gap, and the first bright exciton energy as a function of k-points, cutoff, and number of BSE bands, and justify the 4×4×1 supercell for phonons.","section":"Sec. 2 (Computational Methods)"},{"comment":"The optical absorption onsets are central to the main claim (ultraviolet-to-infrared tunability), but they inherit two approximations that are not benchmarked: the rigid scissor shift is calibrated only to HSE06 single-particle gaps, and the BSE calculation uses a modest number of bands (9 occupied, 9 unoccupied) with a 10–13 k-point mesh. The authors do not report a BSE calculation for h-BN with the same settings to validate the methodology against a known experimental/calculated exciton energy. The excitonic series, especially the lowest bright exciton in PP-BN (0.684 eV), is likely sensitive to both the scissor magnitude and the number of virtual orbitals included. Please add a validation case (e.g., monolayer h-BN BSE with identical parameters) and a convergence test on the number of BSE bands/k-points, or state more explicitly the expected uncertainty in the reported peak positions.","section":"Sec. 3.5 (Optical response)"}],"minor_comments":[{"comment":"The sentence describing the independently corroborating phonon analysis appears twice verbatim ('The same angular softening is independently corroborated by the phonon analysis...'). Remove the duplicate.","section":"Sec. 3.3"},{"comment":"Typographical issues: 'out-of-planep z' is missing a space, and '2D-dimensional boron nitride' should read 'two-dimensional boron nitride'.","section":"Abstract and Sec. 1"},{"comment":"The caption labels the second panel as 'POP-BN'; the text and elsewhere use PP-BN. Please harmonize.","section":"Fig. 7 caption"},{"comment":"Equation (4) and (5) use the notation X = C11C22 − C12^2; the expressions are standard but the derivation or the reference for the anisotropic elasticity formulas could be stated more clearly for readers not familiar with the Cadelano et al. formalism.","section":"Sec. 2"}],"recommendation":"major_revision","confidential_remarks":"The paper is a competent computational screening study, and the qualitative picture is believable. My main concern is that the abstract and conclusions overreach the evidence for 'viable' materials: the kinetic stability question is real for polymorphs lying 0.6–0.8 eV/atom above the ground state. The authors should either add barrier/higher-temperature AIMD evidence or soften the claim. The lack of convergence tests is also unusual for a paper reporting quantitative optical thresholds; a short benchmark section would materially increase trust. I do not see this as a reject: the system, methodology, and conclusions are within the journal's scope and the requested additions are straightforward."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The paper does what it says: it transfers the pentaoctite and pop lattice motifs—already studied in C, Si, Ge, Sn, P, As, Sb, and Bi—to BN and shows they sit in local minima. No imaginary phonons, positive elastic constants, and a 10 ps AIMD run that doesn't fall apart. That is a legitimate new material prediction. The electronic structure work is internally consistent: indirect gaps of 3.26 and 2.59 eV at HSE06, pz-dominated band edges, strong excitonic effects with first bright absorption around 1.6–1.7 eV for PO-BN and 0.68–0.82 eV for PP-BN. If those numbers hold, lattice engineering alone buys a wide spectral range in one chemical system, which is a useful result for 2D optoelectronics, even if not a paradigm shift.\n\nThe authors are honest about the big caveat: both phases are metastable by 644–762 meV/atom relative to h-BN. They also disclose the scissor correction in the BSE calculations, which is standard practice when matching HSE06 gaps. The comparison to other known metastable carbon allotropes (penta-graphene, biphenylene network) is fair context. I don't see a load-bearing logical error.\n\nWhere the paper overreaches is the word \"viable.\" The AIMD is 10 ps at one temperature, 300 K. That can show a local minimum doesn't spontaneously collapse on a picosecond timescale, but it says nothing about barriers to transformation into h-BN. With ΔE in the 0.6–0.8 eV/atom range, you need some estimate of the activation barrier or at least elevated-temperature simulations before calling these thermally stable viable materials. The authors assert the criterion in Sec. 3.1 rather than demonstrate it. That's a real soft spot, but it's fixable: a NEB calculation or even a few hundred ps at higher T would sharpen the claim.\n\nSecond soft spot: the quantitative optical onsets rest on a limited BSE setup—9 occupied and 9 unoccupied bands, TDA, one scissor shift per material, no convergence tests reported. That's enough for a qualitative trend (redshift from UV to IR), but I would not etch the 0.684 eV number into stone yet. The reader's report also flags missing input data and code, which matters for reproducibility; the authors should at least provide structural files and convergence data.\n\nNone of this is fatal. The core prediction—two new BN polymorphs that are metastable but dynamically and mechanically stable—is likely correct. The paper deserves a serious referee, and a revision that adds barrier estimates, longer/hotter AIMD, and convergence checks would strengthen it considerably.","headline":"A solid, honest DFT prediction of two new BN polymorphs whose 'viable material' claim outruns the evidence: 10 ps AIMD at one temperature and no barrier calculation.","tokens_in":12722,"tokens_out":2261,"would_cite":true,"duration_ms":25447,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Pentaoctite-BN and pop-BN monolayers are predicted to be metastable yet dynamically stable indirect-gap semiconductors whose strong excitons shift optical absorption from ultraviolet to visible and telecom infrared.","keywords":["pentaoctite-BN","pop-BN","boron nitride polymorphs","metastable 2D materials","indirect-gap semiconductor","excitonic effects","elastic anisotropy","first-principles"],"falsifier":"Compute the minimum-energy path connecting PO-BN and PP-BN to h-BN using an appropriate transition-state search; if the barrier is less than a few hundred meV per atom, the claimed experimental viability collapses. Alternatively, run AIMD at a few hundred kelvin higher and look for bond breaking, ring reconstruction, or conversion toward h-BN.","tokens_in":11791,"feed_emoji":"🔬","tokens_out":6264,"duration_ms":58604,"temperature":0.7,"pith_summary":"This paper proposes two new boron nitride monolayers built from pentagon and octagon rings instead of hexagons. It argues that despite being less stable than hexagonal BN by 644 and 762 meV per atom, both lattices are genuine local minima: no imaginary phonons appear, elastic constants satisfy stability criteria, and a 10 ps simulation at 300 K leaves the pentagon-octagon networks intact. Both are indirect-gap semiconductors, with HSE06 gaps of 3.26 eV and 2.59 eV, and both show strong excitonic effects. The key payoff is spectral tuning: including electron-hole interactions places the first bright absorption of PO-BN in the visible-near-infrared region and of PP-BN near 0.68-0.82 eV, in the short-wavelength infrared including the 1550 nm telecom window. If correct, this means BN chemistry can span ultraviolet-to-infrared frequencies just by changing the lattice architecture.","feed_headline":"Stable BN monolayers push optical response into the infrared","feed_subtitle":"Pentaoctite-BN and pop-BN are indirect-gap semiconductors predicted to be metastable yet mechanically and dynamically sound.","key_machinery":"The load-bearing structural motif is the pentagon-octagon ring network. In a binary B-N lattice, pentagons force homonuclear B-B and N-N bonds, and the way these bonds are distributed across rings controls the relative stability of the two polymorphs. The electronic/optical argument is carried by out-of-plane pz states: N-pz dominates the valence band top, B-pz the conduction band bottom, and their Coulomb interaction is strong enough that the Bethe-Salpeter optical gap lies about 1.8-2.0 eV below the independent-particle gap. Elastic anisotropy is traced to how the rings are tilted relative to the cell axes, quantified through the angular dependence of Young's modulus and Poisson's ratio.","core_discovery":"The central claim is that the pentagon-octagon network, previously explored in carbon and other elements, can be transferred to boron nitride without destroying semiconducting integrity. Because odd-membered rings force B-B and N-N bonds, the structures pay an energetic penalty of 644-762 meV per atom relative to h-BN, but that penalty is structurally well-defined: PO-BN prefers the weaker B-B bonds in the octagonal rings and N-N bonds in the pentagonal rings, while PP-BN has no such configurational freedom. The resulting monolayers satisfy dynamical, mechanical, and thermal stability criteria; their band edges are pz-dominated, with N-pz at the valence top and B-pz at the conduction bottom;","pith_inferences":["A direct extension of this work would be to compute the minimum-energy pathway from PO-BN or PP-BN to h-BN; a low barrier would falsify the long-lived metastability claim, while a barrier above roughly 1 eV per atom would make these phases isolable in low-temperature growth.","The same pentagon-octagon design could be tested in other binary honeycomb insulators such as AlN or GaN monolayers, asking whether the redshifted exciton series and polarization anisotropy persist under stronger ionicity.","The roughly 130 meV splitting between x- and y-polarized excitons implies that polarized photoluminescence on a single-domain crystal could distinguish the two phases experimentally without needing atomic-resolution imaging.","Because the paper applies a scissor correction to align the optical calculation with the hybrid-functional gap, a plotted absorption spectrum could be misleading if the correction is not truly rigid; an experimental test should compare both absorption onset and higher-energy peak positions."],"forward_implications":["If correct, PO-BN and PP-BN are concrete experimental targets whose near-degenerate high-frequency stretching modes (near 1503 and 1510 cm-1) provide a Raman/IR fingerprint distinct from h-BN.","The combination of strong excitons and in-plane anisotropy makes these monolayers candidate platforms for polarization-sensitive photodetection and optical modulation in the visible and near-infrared.","The 0.684 eV and 0.816 eV bright excitons of PP-BN sit near the 1550 nm telecommunications window, extending BN-based photonics into the infrared.","Tensile strain reduces the energy separation from h-BN without inverting it, suggesting strain can be used to tune, though not eliminate, the metastability penalty."],"fun_headline_variants":["Non-hexagonal BN monolayers tune light into infrared","Pentaoctite BN: stable, metastable, and IR-tunable","BN sheets with odd rings go infrared","Pentaoctite-BN and pop-BN: stable semiconductors for IR"],"cache_read_input_tokens":2304,"weakest_assumption_plain":"The paper's conclusion that the two monolayers are 'viable' and 'thermally stable' rests on a single 10 ps molecular dynamics run at 300 K, with no computed kinetic barrier separating them from h-BN; if that barrier is low, long-lived metastability is not established.","fun_headline_variants_meta":{"raw":{"variants":["Non-hexagonal BN monolayers tune light into infrared","Pentaoctite BN: stable, metastable, and IR-tunable","BN sheets with odd rings go infrared","Pentaoctite-BN and pop-BN: stable semiconductors for IR"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000192,"raw_usage":{"total_tokens":1184,"prompt_tokens":748,"completion_tokens":436,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":492,"completion_tokens_details":{"reasoning_tokens":376}},"tokens_in":492,"tokens_out":436,"duration_ms":5053,"temperature":1.0,"reasoning_tokens":376,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-01T05:45:59.884336+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Compute the minimum-energy path connecting PO-BN and PP-BN to h-BN using an appropriate transition-state search; if the barrier is less than a few hundred meV per atom, the claimed experimental viability collapses. Alternatively, run AIMD at a few hundred kelvin higher and look for bond breaking, ring reconstruction, or conversion toward h-BN.","supporting_citations":[],"review_version":1}