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REVIEW 4 major objections 5 minor 21 references

Comment on 'Anomalies in the Electronic Stopping of Slow Antiprotons in LiF', arXiv:2501.14381

T0 review · 4 major / 5 minor · reviewed 2026-08-16 · deepseek-v4-flash

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Pith's one-line read This comment argues that the anomalies reported in the stopping of slow antiprotons in LiF are artifacts: the disputed curve misses measured data by up to a factor of 3, and the incommensurate-trajectory method can carry a 43% mean error.

desk verdict This comment makes a plausible case that PRL134's low-velocity antiproton stopping curve is too low, but its strongest quantitative claim leans on an unpublished data rescaling and an uncertain inference about trajectory sampling. read the letter →

arxiv 2504.21839 v1 pith:NPIC3ZK5 submitted 2025-04-30 cond-mat.other physics.atom-ph

G. Schiwietz , P.L. Grande This is my paper · ORCID
classification cond-mat.otherphysics.atom-ph PACS 34.50.Bw
keywords electronicstoppingantiprotonslithiumfluoridetime-dependentdensityfunctionaltheoryadiabaticionizationmodelincommensuratetrajectorypowerlow-velocityions
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

This comment tries to establish that the anomalies in the electronic stopping of slow antiprotons in LiF reported in the commented Letter are not a genuine physical effect. It argues that the Letter's low-velocity stopping curve deviates from the published experimental antiproton data by up to a factor of 3, while the Adiabatic Ionization Model and an earlier real-time time-dependent density-functional calculation reproduce the measurements. The main technical accusation is that the Letter used a single incommensurate trajectory of finite length, and the authors show with histograms that such a trajectory can carry a 43% mean statistical error, or as much as 100% for the particular golden-ratio direction, depending on the starting point. A secondary target is the Letter's use of a Coulomb pseudopotential, which may suppress long-range dipole contributions to the energy loss. If the comment is right, the reported anomalies are sampling artifacts plus pseudopotential artifacts rather than new physics.

What carries the argument

The load-bearing mechanism is the Adiabatic Ionization Model (AIM): the stopping power $S_e(v) = \pi P_{\mathrm{cont}}\Delta E_{\mathrm{trans}} b_c(v)^2$, where $b_c(v)$ is the largest impact parameter at which half the collisional energy broadening $\Gamma(v)/2$ crosses the antiproton-lowered adiabatic excitation gap of LiF. The gap curve comes from self-consistent cluster calculations showing that the F-2p orbital is promoted until the gap vanishes near $R \approx 2$ a.u. The same $b_c=2$ a.u. cutoff is then used as a simplified collision statistic in histograms for incommensurate trajectories, which is what produces the 43% versus 12% mean-error contrast between two trajectory directions.

What would settle it

Rerun the criticized calculation with a large set of random incommensurate starts (say 100) and the same pseudopotential: if the anomalous low-velocity knee persists in the averaged stopping, the sampling-artifact explanation is wrong. Conversely, rerunning with the pseudopotential singularity removed should change the stopping by roughly 20% at high velocities if the pseudopotential critique is right.

Watch

Extended reading notes

Core claim

On the paper's own terms, the central claim is that the anomalies reported for slow antiprotons in LiF are not physical. The comment compares the criticized real-time TDDFT curve with corrected experimental data and finds deviations that reach a factor of 3 at low speeds, whereas the Adiabatic Ionization Model, built from self-consistent adiabatic excitation thresholds and collisional broadening, reproduces the data below about 0.5 a.u. It further argues that the incommensurate-trajectory method, if used with a single trajectory of about 48 Å, has large statistical fluctuations: with a fixed critical impact parameter $b_c=2$ a.u., the golden-ratio trajectory direction has a 43% mean error and can miss all close collisions (error $-100\%$), so the knee-like anomaly in the commented Letter may be a sampling artifact. The comment also targets the pseudopotential: a Coulomb pseudopotential that removes the singularity or suppresses the long-range dipole interaction can remove about 20% of the stopping at high velocities and far more at low velocities.

Load-bearing premise

The quantitative part of the critique assumes that the criticized paper used one (or very few) incommensurate trajectories and that the energy-loss statistics can be modeled by a fixed critical impact parameter of $b_c=2$ a.u.; if more trajectories were sampled, or if the real impact-parameter cutoff differs, the estimated 43% mean error and 100% worst-case error do not transfer.

Editorial extensions

If this is right

  • The low-velocity knee reported for antiprotons in LiF should not be cited as evidence for anomalous stopping physics if it disappears once many trajectories are averaged.
  • The Adiabatic Ionization Model, with a nearly constant energy loss below roughly $v=0.3$ a.u. down to the capture limit, becomes the working description of low-velocity antiproton stopping in LiF.
  • Incommensurate-trajectory calculations of stopping in crystals should report convergence over at least ten independent trajectories to reach few-percent accuracy.
  • The choice of trajectory direction matters: a golden-ratio incommensurate direction can substantially worsen the sampling error relative to a generic direction.
  • Pseudopotential treatments of antiprotons need to be checked for removal of the Coulomb singularity and for suppression of the long-range dipole interaction, which materially change the stopping.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • I would infer that the same single-trajectory sampling critique applies to any incommensurate-trajectory stopping calculation with finite path length, not only to LiF, whenever the energy loss is dominated by rare close collisions.
  • A decisive test would be to rerun the criticized calculation with 100 random starting points and the same pseudopotential: the comment's histogram model implies the stopping estimate should scatter by tens of percent, which would show up as a spread in the extracted slope.
  • If the pseudopotential critique is correct, the reported anomaly should be sensitive to the potential's core treatment; varying the pseudopotential in a controlled way would separate sampling error from interaction error.
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Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

4 major / 5 minor

Summary. This manuscript is a Comment on arXiv:2501.14381 / Phys. Rev. Lett. 134, 076401 (2025), which reported anomalies in the electronic stopping of slow antiprotons in LiF. The authors present calculations with their Adiabatic Ionization Model (AIM), compare them with CERN experimental data and with earlier rt-TDDFT results, and argue that the PRL134 results deviate from experiment by up to a factor of 3 at low velocities. They further argue that the PRL134 anomalies likely arise from the use of a single incommensurate trajectory (yielding large statistical errors) and from the use of a local Coulomb pseudopotential, and they criticize statements in PRL134 about antiproton capture, the Horsfield model, and resonance effects.

Significance. If the quantitative claims are correct, the comment would show that a published PRL contains serious artifacts and would support AIM as a better low-velocity description. The finite-length trajectory statistics presented in Figs. 4 and 5 are a useful illustration of potential sampling errors. However, the strongest numerical claim (factor of 3) depends on an unpublished data rescaling, and the trajectory-count inference is uncertain; therefore the overall significance depends on further documentation.

major comments (4)
  1. [Energy Loss Comparison for Antiprotons at low velocities, Fig. 3] The central claim that PRL134 deviates from experiment by up to a factor of 3 is based on multiplying the Møller et al. data by 1.13, and the sole justification is reference [14], described as "publication in preparation, 2025." This is not an available, checkable source; the 1.13 scaling factor, including its velocity dependence and uncertainty, must be documented in the present comment for the factor-of-3 statement to be fully supported.
  2. [On the importance and accuracy of incommensurate trajectories, Figs. 4 and 5] The quoted errors (43% mean for the golden-ratio direction, up to −100%/+47% for individual trajectories) are derived from a simplified AIM step-function model with b_c = 2 a.u. The authors acknowledge that "one cannot be sure" whether PRL134 used a single trajectory; if more than one trajectory was used, or if the real energy-loss statistics differ from this step function, these numbers do not transfer to PRL134. This section should be rewritten as an illustrative uncertainty analysis with explicit conditional language, not as a definitive error estimate for PRL134.
  3. [Collisional Broadening and Antiproton Energy Losses, Eq. (2)] The AIM curve in Fig. 3 depends on three estimated parameters: ΔE_trans = 14.5 eV, P_cont ≈ 58%, and b_c obtained from the crossing in Fig. 2. The paper does not give a sensitivity analysis for these choices, and the same b_c = 2 a.u. is later used for the statistical-error estimate, making part of the critique self-referential. The authors should state whether any AIM parameters are adjusted to reproduce the LiF antiproton data and should show the effect of varying them.
  4. [On the methodology of the PRL134 quantum calculations] The statements that the pseudopotential is "exactly ... responsible for the missing stopping-power contributions of 20% ... and partly for the 200%" and that the supercell "might not represent an undisturbed solid" are speculative hypotheses without supporting calculations. To be load-bearing, these points need to be either demonstrated with test calculations or explicitly labeled as conjectures that require further investigation.
minor comments (5)
  1. [After Fig. 3] The PRL134 curve is referred to as "dashed olive curve" and later as "green dashed curve," while the caption uses "green"; please make the color labels consistent.
  2. [Discussion of AIM agreement] Typo: "resonably" should be "reasonably".
  3. [Eq. (1)] The approximation `≈ E_gap − 1/(R^2 + r_mean^2)^0.5` would benefit from a note that it is a spherically-averaged estimate; as written, the equality of the matrix element with this closed form is not obvious.
  4. [References] Reference [14] is a "publication in preparation"; regardless of the major concern, the manuscript should provide a preprint or an appendix with the scaling details.
  5. [Abstract] The abstract claims "pointing to severe problems," while the body sometimes uses "might be"; the abstract could be more calibrated.

Circularity Check

2 steps flagged · score 4.0 of 10

The headline factor-of-3 disagreement with experiment is anchored in an unpublished 1.13 rescaling by the same authors, and the trajectory-error estimate imports the authors' own AIM threshold into the description of PRL134; the study otherwise compares to external benchmarks and is not severely circular.

  1. self citation load bearing [Section 'Energy Loss Comparison for Antiprotons at low velocities', Fig. 3 paragraph; Ref. [14]]
    "We have scaled the displayed experimental data by Møller et al. [5] for ¯p by a factor of 1.13 to align their proton data with the most precise recent proton measurements (for further details see [14])."

    The headline claim that PRL134 deviates from experiment by up to a factor of 3 is computed against these scaled data. The 1.13 factor is not derived or independently sourced in this paper; it is deferred to [14], which is the authors' own 'publication in preparation, 2025'. The claimed discrepancy therefore depends on an unpublished self-correction of the experimental benchmark, so a key quantitative conclusion is not independently checkable and is effectively assumed via self-citation.

  2. other [Section 'On the importance and accuracy of incommensurate trajectories', Figs. 4-5 paragraphs]
    "Guided by the AIM, we assume a simplified low-energy promotion mechanism that leads to a fixed energy loss below a specific distance-of-closest-approach and otherwise zero energy loss (at larger impact parameters). ... defined by the critical impact parameter b_c = 2a.u."

    The quantitative estimate that a single incommensurate trajectory 'may lead to an extremely large overall error' (43-100%) uses the authors' own Adiabatic Ionization Model as the source of the cross-section input b_c=2 a.u. The same model is then used as the reference curve in Fig. 3. The error estimate is therefore self-referential: it transfers a threshold from the authors' model onto PRL134's simulation rather than deriving PRL134's internal energy-loss statistics. This weakens the transfer, though it is not a by-construction identity.

full rationale

The comment is not a first-principles derivation; it is a comparative critique. Its strongest quantitative assertion (factor-of-3 disagreement with experiment) is anchored in a 1.13 rescaling of the CERN data deferred to an unpublished manuscript by the same authors, which is a load-bearing self-citation and is not independently verifiable. The trajectory-sampling error estimate also imports the AIM critical impact parameter into the description of PRL134's own calculation, making part of the critique model-dependent. However, the paper also makes direct external comparisons to PRL128 rt-TDDFT, CASP, and the raw Møller data, and the AIM parameters (P_cont, Delta E_trans, MCSCF threshold) are fixed from prior work and independent band-structure/density-of-states calculations rather than fitted to the antiproton LiF data. The central claim therefore retains independent content and does not reduce entirely to a fit or self-citation chain. Score 4 reflects one significant self-citation/calibration issue plus a self-referential error estimate, but no by-construction equivalence of the main conclusion to its inputs.

Assumptions & free parameters 6 free parameters · 6 assumptions · 0 invented entities

The quantitative claims are grounded in external experimental data and in a published independent TDDFT calculation, but several load-bearing quantities are chosen by the authors (Pcont, Delta_E_trans, r_mean, b_c, the 1.13 scaling factor) and one key benchmark is unpublished. The statistical critique additionally imports the AIM threshold into a simplified collision model, making the fidelity of the error estimate conditional on AIM's validity.

free parameters (6)
  • Experimental scaling factor = 1.13
    Applied to Møller et al. antiproton data to align their proton data with newer measurements; disclosed but not fully justified, with details deferred to ref. [14].
  • Denominator r_mean = 0.808 a.u.
    From a self-consistent Hartree-Fock-Slater solution for atomic F-; used in Eq. (1) for the perturbative gap estimate.
  • Mean ionization suppression factor Pcont = ~0.58
    Estimated from calculated density of states for the lowest continuum energies; an input to the AIM equation (2).
  • Mean energy transfer Delta_E_trans = 14.5 eV
    Chosen as the experimental unperturbed gap plus 1 eV mean excess energy of ionized electrons.
  • Critical impact parameter b_c = 2 a.u. (model threshold)
    Taken from the MCSCF/AIM crossing threshold and used in the histogram analysis and as the AIM step threshold.
  • Trajectory length L = ~48 angstroms
    Taken from PRL134 Fig. 2 and used in the statistical error estimate for the incommensurate-trajectory method.
assumptions (6)
  • domain assumption The AIM step-function collisional-broadening scheme (Bohr's interaction-time prescription) is a valid approximation for low-velocity ion-solid excitation and energy loss.
    Used to derive the critical impact parameter and the AIM stopping curve in Section 'Collisional Broadening and Antiproton Energy Losses'.
  • domain assumption PRL128 rt-TDDFT results are accurate to about 5% and can serve as an independent benchmark.
    Used to show that PRL134 deviates from an independent calculation; the 5% uncertainty is stated in the text.
  • ad hoc to paper The 1.13 scaling of the CERN experimental data is justified.
    The quantitative factor-of-three deviation depends on this normalization; details are deferred to an unpublished reference.
  • ad hoc to paper The simplified collision model (fixed energy loss for encounters with b below b_c=2 a.u., zero otherwise) captures PRL134's energy-loss statistics.
    This model guides the histogram error estimate; it is not derived from PRL134's own calculations.
  • domain assumption A vanishing excitation gap at R below 2 a.u. (Fermi-Teller promotion) leads to ionization and finite energy loss.
    Basis for the AIM knee and the dotted constant-loss line in Fig. 3.
  • domain assumption No delocalized in-gap state exists in pristine LiF, so the Horsfield model is inapplicable.
    Relies on the absence of reports of such a state and on exciton pinning arguments; used to dismiss PRL134's resonance claims.

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Cite this review

Pith. "Pith review of Comment on 'Anomalies in the Electronic Stopping of Slow Antiprotons in LiF', arXiv:2501.14381." pith.science (2026). https://pith.science/paper/NPIC3ZK5

@misc{pith2026250421839,
  author       = {Pith},
  title        = {Pith review of: Comment on 'Anomalies in the Electronic Stopping of Slow Antiprotons in LiF', arXiv:2501.14381},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/NPIC3ZK5}},
  note         = {Machine review of arXiv:2504.21839}
}
read the original abstract

This work contains detailed discussions on the contents of Phys. Rev. Lett. 134, 076401 (2025), in the following denoted PRL134. In this comment, we revisit and elaborate on the Adiabatic Ionization Model (AIM) for the energy loss of antiparticles in matter, with particular reference to its theoretical foundation as established previously. The AIM framework plays a central role in describing the ionization dynamics in the low-velocity regime considered by the authors of PRL134. Calculated AIM results for the energy loss of antiprotons in LiF crystals are compared to experimental data and different other models, pointing to severe problems of the PRL134 results. Beyond this specific comparative theoretical investigation, we critically examine several statements and assumptions made in PRL134. Certain claims presented therein appear to be inconsistent with established theoretical principles or are insufficiently justified by the data and arguments provided. As such, we believe that further clarification, and in some cases, a more rigorous justification, is necessary to substantiate those points.

Figures

Figures reproduced from arXiv: 2504.21839 by the authors.

Figure 1
Figure 1. FIG. 1. Value of the static excitation-energy gap vs. distance between a point charge [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. FIG. 2. Scheme for extracting the impact-parameter threshold [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. FIG. 3. LiF stopping power vs. ¯p [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figures from the paper (2 more)
Figure 4
Figure 4. Figure 4: FIG. 4. Histogram of the distribution of collision events with F atoms for a large set of straight-line trajectories along an [PITH_FULL_IMAGE:figures/full_fig_p007_4.png]
Figure 5
Figure 5. Figure 5: FIG. 5. Histogram as in Fig. 4, but for the alternative incommensurate [1 [PITH_FULL_IMAGE:figures/full_fig_p007_5.png]

Discussion (0). Continue with ORCID to comment.

Reference graph

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