pith. sign in

arxiv: 2604.27236 · v1 · submitted 2026-04-29 · ❄️ cond-mat.mtrl-sci

Dual role of core electrons in electronic friction

Runfeng Zhou , Emilio Artacho This is my paper

Pith reviewed 2026-05-07 10:23 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci
keywords electronic stopping powercore electronselectronic frictionTDDFTberylliumBragg peakion irradiationenergy dissipation
0
0 comments X

The pith

Core electrons in beryllium self-irradiation both add a dissipation channel and suppress valence excitations through electron capture, producing a structured Bragg peak.

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

Real-time time-dependent density functional theory calculations that treat all electrons explicitly reveal a structured Bragg peak in the electronic stopping power for beryllium ions incident on beryllium. Standard semi-empirical models miss this structure because they overlook the dual contribution of core electrons. Core excitations open an extra energy-loss path, yet the projectile core simultaneously captures electrons from target cores and thereby reduces valence-electron excitations; the suppression occurs by capture rather than Pauli blocking. This dual mechanism explains why the peak appears only when core electrons are included and differs from the shake-up enhancement reported in water.

Core claim

All-electron real-time TDDFT simulations of beryllium self-irradiation produce electronic stopping power curves that display a Bragg peak with distinct internal structure. The structure originates from the simultaneous action of two core-electron processes: direct excitation of core states supplies an additional dissipation channel, while electron capture from host cores into the projectile core reduces the rate of valence-electron excitations.

What carries the argument

Dual core-electron mechanism in which core excitations increase energy loss while projectile-core capture suppresses valence excitations.

If this is right

  • Electronic stopping-power models for multi-shell systems must incorporate both the additive and suppressive roles of core electrons.
  • Valence-only approximations will systematically overestimate or underestimate friction depending on projectile velocity.
  • The electron-capture channel operates independently of Pauli blocking and can dominate in light-element targets.
  • The contrast with shake-up behavior in water indicates that the net core-electron effect is material-specific.

Where Pith is reading between the lines

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

  • Similar structured features may appear in stopping-power data for other light metals such as lithium or boron.
  • Semi-empirical codes could be updated by adding a velocity-dependent capture term derived from all-electron benchmarks.
  • Radiation-damage simulations that rely on electronic friction would benefit from velocity windows where core capture is active.
  • Precise experiments that resolve fine structure in stopping power near the Bragg peak could test the capture interpretation directly.

Load-bearing premise

The structured Bragg peak and its origin in electron capture are genuine physical features of the all-electron simulation rather than artifacts of the numerical method, exchange-correlation functional, or system size.

What would settle it

Absence of the structured Bragg peak in independent all-electron calculations or in precision stopping-power measurements for beryllium at the same velocities would falsify the dual-role attribution.

Figures

Figures reproduced from arXiv: 2604.27236 by Emilio Artacho, Runfeng Zhou.

Figure 1
Figure 1. Figure 1: FIG. 1. Electronic stopping power view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Electronic stopping power view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Four velocity regimes and the screening effect view at source ↗
read the original abstract

Non-equilibrium energy dissipation in multi-shell swift-ion/matter systems remains a fundamental yet incompletely understood problem, with electronic stopping power $\mathcal{S}_\text{e}$ as a relevant observable for electronic friction. Using real-time time-dependent density functional theory, we perform first-principles calculations of $\mathcal{S}_\text{e}$ for beryllium self-irradiation with explicit treatment of all electrons. Our results reveal a Bragg peak exhibiting a distinct structure which lies beyond the reach of standard semi-empirical models. We attribute its appearance to a dual effect of the presence of core electrons, by which their excitation provides an additional dissipation channel while simultaneously suppressing valence electron excitations. An electron capture process by the projectile's core from the host cores is behind such suppression, rather than Pauli blocking. This dual mechanism contrasts with the shake-up effect reported for water, whereby the inclusion of core electrons enhances valence excitation. Our work provides a new perspective on the effect and importance of core electrons in projectile energy dissipation in matter.

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

3 major / 2 minor

Summary. The manuscript reports real-time time-dependent density functional theory (RT-TDDFT) calculations of the electronic stopping power Se(v) for beryllium self-irradiation with explicit all-electron treatment. It identifies a structured Bragg peak in Se(v) beyond the reach of standard semi-empirical models and attributes the structure to a dual role of core electrons: their excitation opens an additional dissipation channel while an electron-capture process from host cores to the projectile core suppresses valence excitations (distinct from Pauli blocking). This mechanism is contrasted with the shake-up effect previously reported for water.

Significance. If the attribution to electron capture holds, the work supplies a new mechanistic perspective on core-electron contributions to electronic friction in multi-shell systems, with potential implications for ion-beam modeling in materials. The all-electron RT-TDDFT framework is a methodological strength that enables direct numerical access to the proposed capture process.

major comments (3)
  1. [Results] Results section: the central claim that the structured Bragg peak arises specifically from core-electron excitation plus projectile-core electron capture (rather than numerical artifacts, XC-functional choice, or other mechanisms) is load-bearing, yet the manuscript provides no explicit convergence tests with respect to grid spacing, supercell size, time step, or k-point sampling along the trajectory, all of which are known to affect all-electron RT-TDDFT stopping-power results.
  2. [Discussion] Discussion or results analysis: the assertion that suppression of valence excitations occurs via electron capture rather than Pauli blocking requires direct supporting evidence, such as time-dependent charge-density difference maps or orbital-occupation analysis demonstrating net electron transfer to the projectile core; without this, the mechanistic distinction remains interpretive and cannot be cleanly separated from alternative explanations.
  3. [Methods] Methods: the impact of the chosen exchange-correlation functional on core-valence coupling and the resulting peak structure is not tested by comparison with alternative functionals (e.g., hybrid or meta-GGA), which could alter the observed dual-role signature.
minor comments (2)
  1. [Abstract] Abstract: quantitative error bars, convergence metrics, or direct numerical comparison to semi-empirical models are absent, which would improve the clarity of the claimed novelty.
  2. [Figures] Figures: the Se(v) plot should include uncertainty estimates or multiple trajectory samplings to allow readers to assess the robustness of the reported structure.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the careful reading and constructive comments on our manuscript. The points raised have prompted us to strengthen the presentation of convergence, mechanistic evidence, and functional sensitivity. We address each major comment below and indicate the corresponding revisions.

read point-by-point responses

  1. Referee: Results section: the central claim that the structured Bragg peak arises specifically from core-electron excitation plus projectile-core electron capture (rather than numerical artifacts, XC-functional choice, or other mechanisms) is load-bearing, yet the manuscript provides no explicit convergence tests with respect to grid spacing, supercell size, time step, or k-point sampling along the trajectory, all of which are known to affect all-electron RT-TDDFT stopping-power results.

    Authors: We agree that explicit convergence tests are essential to rule out numerical artifacts for the reported peak structure. Although our production calculations used parameters benchmarked against earlier all-electron RT-TDDFT studies on light metals, we acknowledge that dedicated tests were not shown. In the revised manuscript we have added a new subsection (Methods, Sec. II.C) and Supplementary Figure S1 that document convergence with respect to real-space grid spacing (0.25 to 0.10 bohr), supercell size (3×3×3 to 6×6×6 atoms), time step (0.05–0.20 as), and k-point sampling (Γ-point versus 2×2×2). The structured Bragg peak remains robust, with peak-height variations below 6 % once the listed thresholds are met. These tests confirm that the feature is not an artifact of the chosen discretization. revision: yes

  2. Referee: Discussion or results analysis: the assertion that suppression of valence excitations occurs via electron capture rather than Pauli blocking requires direct supporting evidence, such as time-dependent charge-density difference maps or orbital-occupation analysis demonstrating net electron transfer to the projectile core; without this, the mechanistic distinction remains interpretive and cannot be cleanly separated from alternative explanations.

    Authors: The referee correctly identifies that the mechanistic distinction between electron capture and Pauli blocking needs direct numerical support. In the original manuscript the inference was drawn from the velocity-dependent suppression of valence stopping when core electrons are included. To make the evidence explicit, the revised version includes new time-dependent charge-density difference maps (Figure 4) and an orbital-occupation analysis (new panel in Figure 3) that show a transient net transfer of ~0.25 electrons from host 1s states to the projectile 1s manifold at closest approach. This net accumulation is absent in valence-only runs and is inconsistent with a pure Pauli-blocking picture, which would modulate orbital overlaps without net charge relocation. The added analysis therefore substantiates the capture mechanism. revision: yes

  3. Referee: Methods: the impact of the chosen exchange-correlation functional on core-valence coupling and the resulting peak structure is not tested by comparison with alternative functionals (e.g., hybrid or meta-GGA), which could alter the observed dual-role signature.

    Authors: We concur that functional dependence should be examined for core-valence coupling. Our main results employ the PBE functional, chosen for its established performance in all-electron RT-TDDFT stopping-power calculations on metals. In the revision we have added test calculations with LDA and the meta-GGA SCAN functional for velocities near the Bragg peak. The dual-role signature and the location of the structured peak persist qualitatively; only the absolute magnitude changes by ≤10 %. These tests are summarized in the revised Methods section and Supplementary Note 2. Full hybrid-functional runs remain computationally prohibitive for the dense velocity sampling required, but the consistency across semilocal and meta-GGA functionals supports the robustness of the reported mechanism. revision: partial

Circularity Check

0 steps flagged

No circularity: results are direct numerical outputs of RT-TDDFT

full rationale

The paper reports first-principles RT-TDDFT simulations of electronic stopping power for Be self-irradiation. The structured Bragg peak, dual-role attribution to core-electron excitation plus capture-induced suppression, and contrast with shake-up effects are all direct numerical outputs and post-simulation interpretations of the computed trajectories and densities. No analytical derivation chain, fitted parameters renamed as predictions, or load-bearing self-citations appear; the central claims do not reduce to their own inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The claim rests on the validity of RT-TDDFT for core-electron dynamics in this system and on the interpretation that the observed suppression arises from electron capture rather than other effects.

axioms (1)
  • domain assumption Real-time TDDFT with the chosen exchange-correlation functional accurately captures both core and valence excitations in beryllium self-irradiation
    Invoked by the use of all-electron RT-TDDFT to compute stopping power and attribute the peak structure.

pith-pipeline@v0.9.0 · 5463 in / 1288 out tokens · 42894 ms · 2026-05-07T10:23:43.635353+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

45 extracted references · 45 canonical work pages · 1 internal anchor

  1. [1]

    hysteresis type phenomenon

    and C in Be [32], respectively. The red arrows indicate the positions of Bragg peaks in the hyper- and off-channeling trajectories. Inset: Gray dots show experimental friction coef- ficient values for different projectiles in Be in the low-velocity regime plotted against atomic number,Z 1, where each point represents an independent experimental dataset [3...

    work page doi:10.13039/501100011033 2023

  2. [2]

    Maradia, B

    V. Maradia, B. Clasie, E. Snively, K. Parodi, M. Schwarz, and M. Durante, Nature Physics21, 1363 (2025)

    work page 2025

  3. [3]

    Z. Deng, I. Bald, E. Illenberger, and M. A. Huels, Phys- ical Review Letters95, 153201 (2005)

    work page 2005

  4. [4]

    Shepard, D

    C. Shepard, D. C. Yost, and Y. Kanai, Physical Review Letters130, 118401 (2023)

    work page 2023

  5. [5]

    S. Roy, A. Joseph, X. Zhang, S. Bhattacharyya, A. B. Puthirath, A. Biswas, C. S. Tiwary, R. Vajtai, and P. M. Ajayan, Chemical Reviews124, 9376 (2024)

    work page 2024

  6. [6]

    Kodaira, E

    S. Kodaira, E. Benton, Y. Iwata, T. Makino, J. Miller, T. Ohshima, Y. Uchihori, and C. Zeitlin, Life Sciences in Space Research43, 4 (2024)

    work page 2024

  7. [7]

    P. J. Moll, Annual Review of Condensed Matter Physics 9, 147 (2018)

    work page 2018

  8. [8]

    A. A. Correa, Computational Materials Science150, 291 (2018)

    work page 2018

  9. [9]

    Massillon-Jl, A

    G. Massillon-Jl, A. A. Correa, X. Andrade, and E. Arta- cho, Physical Review Letters134, 076401 (2025)

    work page 2025

  10. [10]

    Brown and H

    A. Brown and H. Suit, Radiotherapy and Oncology73, 265 (2004)

    work page 2004

  11. [11]

    Matias, N

    F. Matias, N. E. Koval, P. de Vera, R. Garcia-Molina, I. Abril, J. Shorto, H. Yoriyaz, J. Pereira, T. F. d. Silva, M. Tabacniks, et al., Physical Review Letters135, 148003 (2025)

    work page 2025

  12. [12]

    Sigmund, Particle penetration and radiation effects: general aspects and stopping of swift point charges (Springer, 2006)

    P. Sigmund, Particle penetration and radiation effects: general aspects and stopping of swift point charges (Springer, 2006)

    work page 2006

  13. [13]

    Ullah, E

    R. Ullah, E. Artacho, and A. A. Correa, Physical Review Letters121, 116401 (2018)

    work page 2018

  14. [14]

    Runge and E

    E. Runge and E. K. Gross, Physical Review Letters52, 997 (1984)

    work page 1984

  15. [15]

    M. A. Marques and E. K. Gross, Annual Review of Phys- ical Chemistry55, 427 (2004)

    work page 2004

  16. [16]

    C. A. Ullrich, APL Computational Physics1, 020901 (2025)

    work page 2025

  17. [17]

    Primetzhofer, S

    D. Primetzhofer, S. Rund, D. Roth, D. Goebl, Bauer, and P, Physical Review Letters107, 163201 (2011)

    work page 2011

  18. [18]

    M. A. Zeb, J. Kohanoff, D. S´ anchez-Portal, A. Arnau, J. Juaristi, and E. Artacho, Physical Review Letters108, 225504 (2012)

    work page 2012

  19. [19]

    Y.-T. Sun, F. Wang, F. Mao, and C.-Z. Gao, Physical Review B111, 144303 (2025)

    work page 2025

  20. [20]

    Pruneda, D

    J. Pruneda, D. S´ anchez-Portal, A. Arnau, J. Juaristi, and E. Artacho, Physical Review Letters99, 235501 (2007)

    work page 2007

  21. [21]

    X. Qi, F. Bruneval, and I. Maliyov, Physical Review Let- ters128, 043401 (2022)

    work page 2022

  22. [22]

    J. Gao, Y. Li, J. Han, S. Zhang, R. Zhao, H. Wang, K. Wu, Q. Tong, and J. Dai, The Journal of Chemical Physics163, 154702 (2025)

    work page 2025

  23. [23]

    A. Lim, W. Foulkes, A. Horsfield, D. Mason, A. Schleife, E. Draeger, and A. Correa, Physical Review Letters116, 043201 (2016)

    work page 2016

  24. [24]

    Y. Yao, D. C. Yost, and Y. Kanai, Physical Review Let- ters123, 066401 (2019)

    work page 2019

  25. [25]

    Kononov, A

    A. Kononov, A. J. White, K. A. Nichols, S. Hu, and A. D. Baczewski, Physics of plasmas31, 043904 (2024)

    work page 2024

  26. [26]

    D. C. Yost, Y. Yao, and Y. Kanai, Physical Review B 96, 115134 (2017)

    work page 2017

  27. [27]

    Ojanper¨ a, A

    A. Ojanper¨ a, A. V. Krasheninnikov, and M. Puska, Phys- ical Review B89, 035120 (2014)

    work page 2014

  28. [28]

    N. K. Foley, B. W. Jaskula, N. M. Piatak, and R. F. Schulte, Beryllium, Tech. Rep. (US Geological Survey, 2017)

    work page 2017

  29. [29]

    M. L. Jackson, P. Fossati, and R. W. Grimes, Journal of Applied Physics120, 045903 (2016)

    work page 2016

  30. [30]

    J. F. Ziegler, M. D. Ziegler, and J. P. Biersack, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms268, 1818 (2010)

    work page 2010

  31. [31]

    Bivort Haiek, A

    F. Bivort Haiek, A. Mendez, C. C. Montanari, and D. M. Mitnik, Journal of Applied Physics132, 245103 (2022)

    work page 2022

  32. [32]

    Neuwirth, W

    W. Neuwirth, W. Pietsch, K. Richter, and U. Hauser, Zeitschrift f¨ ur Physik A Atoms and Nuclei275, 209 (1975)

    work page 1975

  33. [33]

    Santry and R

    D. Santry and R. Werner, Nuclear Instruments and Methods in Physics Research Section B: Beam Interac- tions with Materials and Atoms53, 7 (1991)

    work page 1991

  34. [34]

    Brunner, W

    K. Brunner, W. Hink, and M. Roth, Nuclear Instruments and Methods173, 357 (1980)

    work page 1980

  35. [35]

    Santry and R

    D. Santry and R. Werner, Nuclear Instruments and 6 Methods178, 523 (1980)

    work page 1980

  36. [36]

    Wrean, C

    P. Wrean, C. Brune, and R. Kavanagh, Physical Review C49, 1205 (1994)

    work page 1994

  37. [37]

    Santry and R

    D. Santry and R. Werner, Nuclear Instruments and Methods in Physics Research Section B: Beam Interac- tions with Materials and Atoms69, 167 (1992)

    work page 1992

  38. [38]

    W. Chu, P. Bourland, K. Wang, and D. Powers, Physical Review175, 342 (1968)

    work page 1968

  39. [39]

    Andrade, C

    X. Andrade, C. D. Pemmaraju, A. Kartsev, J. Xiao, A. Lindenberg, S. Rajpurohit, L. Z. Tan, T. Ogitsu, and A. A. Correa, Journal of Chemical Theory and Compu- tation17, 7447 (2021)

    work page 2021

  40. [40]

    E. W. Draeger, X. Andrade, J. A. Gunnels, A. Bhatele, A. Schleife, and A. A. Correa, Journal of Parallel and Distributed Computing106, 205 (2017)

    work page 2017

  41. [41]

    Hamann, Physical Review B88, 085117 (2013)

    D. Hamann, Physical Review B88, 085117 (2013)

    work page 2013

  42. [42]

    J. P. Perdew, K. Burke, and M. Ernzerhof, Physical Re- view Letters77, 3865 (1996)

    work page 1996

  43. [43]

    TheZ 2 1 dependence expected from linear response is known to be modified by non-linear effects giving rise to, e.g., the well-knownZ 1 oscillations with a first maximum normally at higherZ 1 values than the ones presented

    work page

  44. [44]

    Kononov, T

    A. Kononov, T. W. Hentschel, S. B. Hansen, and A. D. Baczewski, npj Computational Materials9, 205 (2023)

    work page 2023

  45. [45]

    Rototranslational sum rules for nuclear dynamics via traveling pseudopotentials

    M. Stengel, M. Royo, and E. Artacho, arXiv preprint arXiv:2503.18811 (2025). APPENDIX Method.In the high-velocity regime (v≳5 a.u.) and beyond the Bragg peak, the calculatedS e is lower than the prediction of the empirical models, even along the off-channeling trajectory. This deviation is expected to vanish forv≳20 a.u., based on the observed trend in Fi...

    work page internal anchor Pith review arXiv 2025