{"id":"e842ffd5-be4a-465e-9442-f610a8a1ee5b","arxiv_id":"1908.10946","paper_version":3,"verdict":"ACCEPT","confidence":"HIGH","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Infinite-layer nickelates have cuprate-like electronic parameters, including a large t'/t ratio and similar pd/pp hoppings, but a much larger charge-transfer energy.","lead":"This paper uses computer calculations to compare the electronic structure of newly discovered nickelate superconductors with copper-oxide superconductors. It finds the nickelates share key electron-hopping patterns that should help superconductivity, though a larger energy gap may explain their lower temperature.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The central t'/t comparison may be an artifact of omitting the La-5d states that cross EF in LaNiO2; the paper's own Slater-Koster rms error (331 meV vs 174 meV) flags this omission.","rationale":"The reader's weakest assumption is exactly the omission of La-5d states from the low-energy tight-binding and Wannier models. This is the most load-bearing part of the central claim because the headline implication (large t'/t should be conducive to superconductivity) depends on quantitative hopping ratios extracted from those models. The paper's own Supplemental Material provides direct evidence of the problem: the Slater-Koster rms error for LaNiO2 is nearly twice that for CaCuO2, attributed to neglected La-d states. In LaNiO2 these states cross EF, so they are not a high-energy remote manifold that can be safely integrated out; the effective one-band parameters may be renormalized or contaminated. The Wannier fits are acknowledged to be non-unique, and the six-parameter fit's quality is not reported, so the central t'/t value lacks a key robustness check. I would not reject the paper: the comparative electronic-structure study is careful, reproducible in principle, and the authors disclose the limitation. However, the verdict should be conditional on the proposed inclusion of La-d states in a downfolding test. If the test preserves t'/t and Delta, the paper's conclusion stands; if not, the abstract's central claim needs to be qualified or revised. This is a concrete, falsifiable check rather than a mere expression of doubt.","tokens_in":8487,"tokens_out":7520,"duration_ms":81744,"concrete_test":"Re-run the WIEN2k/Wannier90 workflow for LaNiO2 (with CaCuO2 as a control) using an initial projection that includes La/Ca d states (at least dz2 and dxy) in addition to Ni/Cu-d and O-p orbitals, then downfold to an effective dx2-y2 one-band Hamiltonian (e.g., via Wannier interpolation of the entangled bands). Compare t1, t2, t3, t'/t, and the Wannier d-p on-site splitting to Tables I and II. If t'/t changes by more than about 30% (e.g., from 0.37 to below 0.25) or if Delta drops by more than about 0.5 eV, the abstract-level claim is not robust to the omitted La-d states.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The abstract-level claim that RNiO2 has a cuprate-like t'/t of about 0.37 rests on a six-parameter tight-binding fit to the dx2-y2 band at EF and on Wannier fits that start from five Ni-d and six O-p orbitals. The Supplemental Material reports that the Slater-Koster fit for LaNiO2 has an rms error of 331 meV versus 174 meV for CaCuO2 and states this is 'likely due to not taking into account the influence of the La d states.' In LaNiO2 the La-5d states are not a passive high-energy background: they cross EF, forming the electron pockets at Γ (La-dz2) and A (La-dxy) that self-dope the dx2-y2 Fermi surface. If these states hybridize with the d-p antibonding band, the fitted t1, t2, t3 and the Wannier-derived d-p on-site splitting (Delta = 4.4 eV versus 2.7 eV) can absorb the omitted La-d degrees of freedom. The Wannier transformation is explicitly non-unique ('faithful (though not unique)'), and the paper never reports the rms error of the six-parameter dx2-y2 fit that produces the central t'/t number. A spuriously large longer-range hopping ratio could arise if the fitted band is contaminated by proximity to La-d states. Thus the central quantitative comparison may be an artifact of the orbital basis rather than a robust electronic-structure property of RNiO2.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper revisits the electronic structure of infinite-layer nickelates RNiO2 (R = La, Nd) using DFT (GGA), LDA+U, maximally localized Wannier functions, tight-binding fits, and Slater-Koster fits, comparing them with the cuprate CaCuO2. The central findings are that the pd and pp hopping parameters are similar between the nickelates and cuprates, the t'/t ratio is large (~0.37) for both, the eg splitting is comparable, but the charge-transfer gap Δ is much larger in LaNiO2 (4.4 eV) than in CaCuO2 (2.7 eV). The paper argues that the large t'/t is favorable for superconductivity, the large Δ may account for the reduced Tc, and the La-5d electron pockets self-dope the main Fermi surface. It also presents spin-polarized results, doping studies, and a Hall coefficient analysis.","tokens_in":8724,"tokens_out":8153,"duration_ms":76840,"significance":"If the central electronic-structure comparison is robust, the identification of a cuprate-like t'/t in infinite-layer nickelates is an important step toward understanding superconductivity in these materials. The paper provides a detailed set of fitted parameters in Tables I and II and in the Supplemental Material, allowing direct quantitative comparison, and it interprets these parameters using independent empirical correlations from Pavarini, Sakakibara, and Weber rather than self-referential criteria. The discussion of self-doping, the rigid-band estimate of optimal doping, and the Hall coefficient analysis add value. The principal weakness is that the fits underpinning the central t'/t and Δ claims omit the La-5d states, which the authors themselves acknowledge can affect the fits.","major_comments":[{"comment":"The central claim in the abstract that both materials exhibit a large ratio of longer-range to near-neighbor hopping rests on the six-parameter tight-binding fit to the dx2-y2 band reported in Table I. No rms error or fitting window is reported for this fit. Since the La-5d states cross the Fermi level and the paper states that inclusion of the La/Ca dz2 orbital improves the Wannier fits, the fitted t1, t2, and t3 values could be affected by the omitted La-d degrees of freedom. Please provide the fit error, specify the energy window used, and show how the extracted parameters and the t'/t ratio change when a La dz2 orbital is included in the Wannier basis.","section":"Wannierization"},{"comment":"The Slater-Koster fit for LaNiO2 has an rms error of 331 meV versus 174 meV for CaCuO2, which the authors attribute to the neglect of the La-d states. This large discrepancy raises a parallel concern about the Wannier-derived charge-transfer gap Δ = 4.4 eV in Table II, because that Wannier basis also omits La-d states. Please report whether including the La dz2 orbital changes the on-site energies and hoppings in Table II, and if so, how the comparison with cuprates is modified. Without this information, the robustness of both the large Δ and the large t'/t conclusions is not fully established.","section":"Supplemental Material, Table I"}],"minor_comments":[{"comment":"The first row of Table I is the constant term t0, not the nearest-neighbor hopping t1; please clarify in the caption that t1 is the coefficient of 2[cos(kxa)+cos(kya)] so that the definition of t'/t is unambiguous.","section":"Table I"},{"comment":"The phrase \"including our own [9,11]\" is inaccurate because reference [9] is by Lee and Pickett; only reference [11] is the authors' previous work.","section":"Conclusions"},{"comment":"The sentence \"The energy difference obtained with respect to the non magnetic state is 0.70 meV/Ni and 0.69 meV/Ni with respect to an A-type AFM state\" is ambiguous; please rewrite to state explicitly which state is the lowest and what the energy differences refer to.","section":"Spin-polarized calculations"},{"comment":"The statement that inclusion of the La/Ca dz2 orbital improves the fits is not quantified anywhere in the manuscript; please either provide the resulting changes in the Table II parameters or state explicitly that the reported values are from the basis without La dz2.","section":"Wannierization"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is a solid computational comparison that fits the journal's scope. The La-5d omission is a legitimate concern, but it is addressable with additional fits. The authors should be encouraged to provide the requested error metrics and basis-dependence checks; if those confirm the reported values, the paper would be suitable for publication."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The paper is a straightforward, honest computational comparison, and the new stuff is concrete: Wannier-derived hoppings, on-site energies, and a six-parameter tight-binding fit for LaNiO2 and CaCuO2, giving t'/t around 0.37 in both. The central conclusion—that infinite-layer nickelates have cuprate-comparable pd and pp hoppings and a large t'/t that should be favorable for superconductivity—holds up better than I expected against the main objection I'd raise.\n\nWhat's actually new: the paper explicitly differs from the Lee-Pickett parameterization by including longer-range in-plane hoppings and different interlayer functions, and it gives numbers in tables that are directly reusable. It also quantifies the large charge-transfer gap difference (4.4 vs 2.7 eV for Ni vs Cu) and ties the La-5d self-doping pockets to the Hall sign, which is a nice, falsifiable piece of analysis.\n\nWhere it's soft: the superconductivity implications are extrapolations from cuprate empirical correlations (Pavarini, Sakakibara, Weber), not derived from any nickelate model. The authors are explicit about this, and they even note that the large gap would put RNiO2 outside Weber's bounds, tempering the optimism. That's honest. The stress-test worry—that omitting La-5d from the dx2-y2 fit could inflate t'/t—is plausible in principle but I don't think it lands as a fatal flaw. The dx2-y2 band at the Fermi energy is well separated from the La pockets, and the La-5d hybridization is mostly with dz2, not dx2-y2. The paper acknowledges in the supplemental that the larger Slater-Koster rms error for Ni (331 vs 174 meV) is likely due to neglecting La-5d states. It would be better to report the rms error of the six-parameter fit that produces the headline t'/t, and a test with an explicit La-d basis would strengthen the claim, but this is a completeness issue, not a red flag.\n\nThe magnetic section is thin and correctly notes that the computed C-type AFM order is not seen experimentally. The doping analysis is rigid-band based, which is a standard approximation with acknowledged limits.\n\nCitation pattern is fair; the self-citations are to the relevant prior Lee-Pickett and Botana-Norman papers, and the new parameters are clearly distinguished from that earlier work.\n\nThe paper will be useful to experimentalists and computationalists working on nickelate superconductors as a reference for electronic-structure parameters. It deserves a serious peer review, and I'd accept it, with a request for fit errors and a sensitivity test to La-d inclusion rather than any major revision.","headline":"A careful electronic-structure comparison that delivers new Wannier/tight-binding parameters and a plausible large-t'/t story for nickelates; the La-5d caveat is real but not fatal.","tokens_in":9365,"tokens_out":2293,"would_cite":true,"duration_ms":25334,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Infinite-layer nickelates are plausible cuprate analogs: their key hopping ratios match, and only the much larger charge-transfer gap stands between them and the cuprate recipe for superconductivity.","keywords":["infinite-layer nickelates","cuprate analogs","electronic structure","Wannier functions","tight-binding","charge-transfer gap","superconductivity","t'/t ratio"],"falsifier":"Explicitly include the La-$5d$ orbitals in the Wannier active space and refit the one-band parameters: if $t'/t$ falls well below 0.37 or $\\Delta$ moves toward the cuprate value of 2.7 eV, the comparison collapses. A direct spectroscopic determination of the charge-transfer gap in LaNiO$_2$—near 4.4 eV or near 2.7 eV—would also settle which parameter set describes the physics.","tokens_in":8181,"feed_emoji":"🧲","tokens_out":11057,"duration_ms":94668,"temperature":0.7,"pith_summary":"This paper argues that the newly superconducting infinite-layer nickelates $R$NiO$_2$ ($R$ = La, Nd) are, contrary to earlier doubts, credible cuprate analogs. By fitting the low-energy $d_{x^2-y^2}$ band of LaNiO$_2$ and comparing it with its cuprate counterpart CaCuO$_2$, the authors find that the near-neighbor and longer-range hopping parameters are comparable, giving a large ratio $t'/t \\approx 0.37$ in both families—a ratio empirically associated with high superconducting transition temperatures in cuprates. The decisive difference is the charge-transfer gap, roughly 4.4 eV in the nickelate versus 2.7 eV in the cuprate, which puts $R$NiO$_2$ outside the range previously deemed favorable for superconductivity and may explain why the observed $T_c$ is low. The paper concludes that the large $t'/t$ ratio, together with self-doping by La-$5d$ electron pockets, makes $R$NiO$_2$ a promising platform for further superconductivity studies.","feed_headline":"Nickelates match cuprates' key hopping ratio","feed_subtitle":"t'/t is about 0.37 in both; the much larger nickelate charge-transfer gap may explain its low Tc.","key_machinery":"The load-bearing machinery is a three-level tight-binding analysis of the density-functional band structures: a six-parameter fit to the $d_{x^2-y^2}$ band at the Fermi energy, a maximally localized Wannier-function parametrization of the $d$-$p$ manifold, and Slater-Koster fits seeded by the Wannier values. The cuprate comparison is carried by two derived numbers—the ratio $t'/t = (|t_3|+|t_2|)/|t_1|$, which comes out near 0.37 in both materials, and the charge-transfer gap $\\Delta$, which comes out at 4.4 eV for the nickelate and 2.7 eV for the cuprate—because these are the quantities previously correlated with $T_c$ in cuprates.","core_discovery":"On the paper's own terms, the central discovery is that the electronic-structure parameters that correlate with superconductivity in cuprates split into two sets when carried over to infinite-layer nickelates. The hopping integrals—$pd\\sigma$ about 1.4–1.5 eV, $pp\\sigma$ about 1.2–1.3 eV, and the one-band $t_1,t_2,t_3$—are nearly the same in LaNiO$_2$ and CaCuO$_2$, yielding $t'/t \\approx 0.37$; the $e_g$ splitting is also comparable. But the charge-transfer energy $\\Delta = \\epsilon_d - \\epsilon_p$ is almost twice as large (4.4 eV versus 2.7 eV), and two small La-$5d$ Fermi pockets self-dope the hole-like $d_{x^2-y^2}$ surface. The authors therefore present $R$NiO$_2$ as a cuprate analog in which the parameters that favor superconductivity are present and the main outlier is the large gap, a feature that could account for the reduced $T_c$.","pith_inferences":["Editorial inference: because the large gap and the self-doping both originate in the rare-earth spacer states, substituting different $R$ cations or applying epitaxial strain should tune $\\Delta$ downward; under this paper's logic, such modified nickelates would be predicted to have higher $T_c$.","Editorial inference: applying the same Wannier-to-Slater-Koster comparison to other reduced nickelate families, such as the bilayer La$_3$Ni$_2$O$_6$, would test whether the cuprate-like hopping pattern is a general property of Ni$^{1+}$ square planes.","Editorial inference: the parameter set implies a sharp spectroscopic check—resonant inelastic X-ray scattering should place the Ni charge-transfer excitation near 4.4 eV in LaNiO$_2$, well above the cuprate value, if the paper's $\\Delta$ is right."],"forward_implications":["The large $t'/t$ ratio and comparable $pd$/$pp$ hoppings place $R$NiO$_2$ inside the empirical cuprate window for pairing, so the same descriptors used to rank cuprates by $T_c$ would rank the nickelates as promising superconductors.","Because the La-$5d$ pockets self-dope the hole-like Fermi surface, optimal doping is likely lower than in the cuprates; the rigid-band estimate is about 12% rather than 16%.","Electron doping of $R$NiO$_2$ should be as revealing as electron doping of SrCuO$_2$, which gives the highest $T_c$ among electron-doped cuprates.","If the large charge-transfer gap is what suppresses pairing, the nickelates become a direct testbed for how $\\Delta$ controls $T_c$ in a cuprate-like single-band setting."],"supporting_citations":[{"why":"Supplies the experimental discovery of superconductivity in Sr-doped NdNiO2 that motivates the whole comparison.","marker":"[12]"},{"why":"Supplies the empirical correlation between large t'/t ratios and high Tc in cuprates used to judge the nickelates.","marker":"[13]"},{"why":"Supplies the definition of t'/t as (|t3|+|t2|)/|t1| and the eg-splitting correlation used in the comparison.","marker":"[14]"},{"why":"Supplies the charge-transfer-gap window that RNiO2 falls outside of, framing the paper's central tension.","marker":"[15]"},{"why":"Provides the earlier electronic-structure calculation emphasizing La-5d hybridization that this paper revisits and partially overturns.","marker":"[9]"},{"why":"Supplies the Slater-Koster parameter set for CaCuO2 that the paper extends and improves as the cuprate reference.","marker":"[28]"},{"why":"Provides the zero-doping Hall and transport data used to argue that the large Fermi surface is gapped at low doping.","marker":"[7]"}],"fun_headline_variants":["Same hopping ratio, double the gap: nickelate superconductivity","Cuprate-like hopping in nickelates may explain lower Tc","Nickelates hit cuprate-like hopping, but gap is bigger","t'/t ~ 0.37 in both: nickelates and cuprates align"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The argument assumes that the low-energy model built from Ni-$d$ and O-$p$ Wannier functions—omitting the La-$5d$ states that cross the Fermi energy—captures the parameters that control superconductivity; the noticeably worse Slater-Koster fit in the nickelate (rms 331 meV versus 174 meV) is a warning that this assumption may be too strong.","fun_headline_variants_meta":{"raw":{"variants":["Same hopping ratio, double the gap: nickelate superconductivity","Cuprate-like hopping in nickelates may explain lower Tc","Nickelates hit cuprate-like hopping, but gap is bigger","t'/t ~ 0.37 in both: nickelates and cuprates align"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000655,"raw_usage":{"total_tokens":2969,"prompt_tokens":885,"completion_tokens":2084,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":501,"completion_tokens_details":{"reasoning_tokens":2005}},"tokens_in":501,"tokens_out":2084,"duration_ms":15844,"temperature":1.0,"reasoning_tokens":2005,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T10:31:34.889321+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Explicitly include the La-$5d$ orbitals in the Wannier active space and refit the one-band parameters: if $t'/t$ falls well below 0.37 or $\\Delta$ moves toward the cuprate value of 2.7 eV, the comparison collapses. A direct spectroscopic determination of the charge-transfer gap in LaNiO$_2$—near 4.4 eV or near 2.7 eV—would also settle which parameter set describes the physics.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the experimental discovery of superconductivity in Sr-doped NdNiO2 that motivates the whole comparison."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the empirical correlation between large t'/t ratios and high Tc in cuprates used to judge the nickelates."},{"cited_title":"Pavarini, I","cited_arxiv_id":null,"evidence_quote":"Supplies the definition of t'/t as (|t3|+|t2|)/|t1| and the eg-splitting correlation used in the comparison."},{"cited_title":"Sakakibara, H","cited_arxiv_id":null,"evidence_quote":"Supplies the charge-transfer-gap window that RNiO2 falls outside of, framing the paper's central tension."},{"cited_title":"For both the AMF and FLL schemes, the value of the magnetic moment at the Ni site increases up to the highest U value used of 6 eV","cited_arxiv_id":null,"evidence_quote":"Provides the earlier electronic-structure calculation emphasizing La-5d hybridization that this paper revisits and partially overturns."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the Slater-Koster parameter set for CaCuO2 that the paper extends and improves as the cuprate reference."},{"cited_title":"Ikeda, Y","cited_arxiv_id":null,"evidence_quote":"Provides the zero-doping Hall and transport data used to argue that the large Fermi surface is gapped at low doping."}],"review_version":1}