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arxiv: 2605.20358 · v2 · pith:KIC6MB5Nnew · submitted 2026-05-19 · ❄️ cond-mat.mtrl-sci · cond-mat.dis-nn· cond-mat.mes-hall

Modeling phase separation in polymer-derived silicon carbonitride ceramics through extended machine learning molecular dynamics

Fabien Mortier , Sylvian Cadars , Olivier Masson , Mauro Boero , Guido Ori , Yun Wang , Samuel Bernard , Assil Bouzid This is my paper

Pith reviewed 2026-05-21 07:24 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci cond-mat.dis-nncond-mat.mes-hall
keywords polymer-derived ceramicssilicon carbonitridephase separationmachine learning interatomic potentialmolecular dynamicsgraphene-like domainsamorphous materialsthermal processing
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The pith

Machine learning molecular dynamics reveals carbon nucleating into graphene-like sheets within the SiCN ceramic matrix during heating.

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

This paper develops a machine learning interatomic potential for Si-C-N-H systems trained on more than 9000 configurations that include amorphous structures, high-temperature states, surfaces, and crystals. The potential supports molecular dynamics simulations of 8000-atom models that track the evolution of polymer-derived silicon carbonitride during thermal processing. These simulations show carbon domains progressively separating from the amorphous matrix to form distinct graphene-like sheets while the surrounding ceramic network remains connected. The resulting structures match experimental atomic pair distribution functions and trace the transformation through rearrangements of defective five- and seven-membered carbon rings into stable six-membered rings.

Core claim

The central discovery is a phase separation process in which carbon domains nucleate from the amorphous SiCN matrix during thermal treatment, forming graphene-like sheets while the integrity of the ceramic network is preserved. Defective five- and seven-membered carbon rings mediate the conversion to stable six-membered aromatic structures. The simulated atomic configurations reproduce experimental pair distribution functions with high fidelity, supplying atomic-scale explanations for the combination of ceramic thermal stability and graphitic features in these materials.

What carries the argument

A machine learning interatomic potential trained on a diversified database of over 9000 configurations that enables large-scale molecular dynamics simulations of 8000-atom SiCNH systems at high temperature.

If this is right

  • The method supplies atomic-level mechanisms for the thermal stability and mixed properties of polymer-derived ceramics.
  • Defective carbon rings are identified as the structural intermediates that enable the transition to ordered graphitic domains.
  • The same potential framework can be applied to other complex amorphous multicomponent systems at experimentally relevant sizes.
  • Microscopic pathways for structural transformation during processing are now accessible for direct comparison with experiment.

Where Pith is reading between the lines

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

  • Processing temperatures or times could be adjusted to control the size and connectivity of the emerging carbon sheets for targeted electrical or mechanical performance.
  • The same simulation approach might be extended to predict how dopants or different polymer precursors alter the phase-separation route.
  • Longer simulation timescales could reveal whether the graphene-like domains continue to grow or stabilize once formed.

Load-bearing premise

The trained machine learning potential reproduces the energies and dynamics of carbon nucleation and ring changes in large systems without large extrapolation errors or missing interactions.

What would settle it

A simulation run at the same temperature and scale that produces no carbon domain nucleation or that yields atomic pair distribution functions clearly different from experimental measurements would falsify the reported phase-separation mechanism.

Figures

Figures reproduced from arXiv: 2605.20358 by Assil Bouzid, Fabien Mortier, Guido Ori, Mauro Boero, Olivier Masson, Samuel Bernard, Sylvian Cadars, Yun Wang.

Figure 1
Figure 1. Figure 1: FIG. 1: Multidimensional scaling 2D projection of the training database using Valle-Oganov fingerprints [ [PITH_FULL_IMAGE:figures/full_fig_p005_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2: Evolution of the loss on the validation set during the training process. The figure shows the two stages of [PITH_FULL_IMAGE:figures/full_fig_p007_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3: Comparison of MLIP-predicted energies and forces with DFT reference values for the test set. [PITH_FULL_IMAGE:figures/full_fig_p008_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4: a) Thermal cycles applied to the 8000-atom models using the MLIP. The extended high-temperature [PITH_FULL_IMAGE:figures/full_fig_p010_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5: Partial pair distribution functions for the 8000-atom models. [PITH_FULL_IMAGE:figures/full_fig_p012_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6: (Top) Configurations of C-C bonds in the final snapshot of models SiCNH8000-Random, SiCNH8000-CNB, [PITH_FULL_IMAGE:figures/full_fig_p014_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: FIG. 7: Evolution of the proportion of carbon atoms in different environments (single, dimers, linear chains, [PITH_FULL_IMAGE:figures/full_fig_p016_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: FIG. 8: (a-f) Atomic configurations illustrating the mechanism of aromatic ring formation from isolated carbon [PITH_FULL_IMAGE:figures/full_fig_p018_8.png] view at source ↗
read the original abstract

Polymer-derived ceramics combine the thermal stability of ceramics with the versatile properties of carbon domains, but modeling their atomic-scale evolution during processing remains elusive due to the limitations of traditional computational methods. To address this issue, here we develop and apply a machine learning interatomic potential for silicon carbonitride-based (Si-C-N-H) systems, trained on a diversified database of over 9000 configurations -- including amorphous models, high-temperature states, surfaces, and crystal structure predictions -- to capture the full complexity of these materials. This potential enables large-scale molecular dynamics simulations of 8000-atom systems revealing the atomic-scale evolution of the polymer-derived ceramic during thermal treatment. A key result of this work is the occurrence of a phase separation where carbon domains progressively nucleate from the amorphous SiCN matrix during thermal processing, forming distinct graphene-like sheets while preserving the integrity of the ceramic network. The resulting models reproduce the experimental atomic pair distribution functions with exceptional fidelity, validating our approach and providing microscopic explanations for the material unique combination of ceramic and graphitic properties. In this process, defective 5- and/or 7-member carbon rings, mediate the transformation to stable 6-member aromatic structures. These findings offer new atomic-scale insights into the thermal stability and structural transformation pathways of polymer-derived ceramics, while our methodology opens avenues for studying complex amorphous systems with first-principles accuracy at experimentally relevant scales.

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

1 major / 2 minor

Summary. The paper develops a machine learning interatomic potential for Si-C-N-H systems trained on a diversified database of over 9000 configurations (including amorphous, high-temperature, surface, and crystal structures). It applies this potential to large-scale MD simulations of 8000-atom polymer-derived SiCN models during thermal processing. The central claim is that carbon domains nucleate from the amorphous matrix to form graphene-like sheets via mediation by defective 5- and 7-membered rings that rearrange into stable 6-membered aromatic structures, while the final atomic configurations reproduce experimental pair distribution functions with high fidelity.

Significance. If the dynamical pathway is faithfully reproduced, the work provides valuable atomic-scale mechanistic insight into phase separation and carbon domain formation in polymer-derived ceramics, explaining their hybrid ceramic-graphitic properties at experimentally relevant scales. The scale-up to 8000-atom systems and reproduction of experimental PDFs are notable strengths that could inform processing strategies.

major comments (1)
  1. [MD simulation results and validation section] The load-bearing claim is that the ML potential correctly drives carbon nucleation and the 5-/7- to 6-membered ring conversion during high-T annealing. However, validation is reported only via reproduction of experimental PDFs for the final structures (Abstract and results on MD trajectories). PDF agreement constrains equilibrium pair correlations but does not test relative energies or barriers of the defective-ring intermediates identified as mediating the transformation, leaving open the possibility that the observed pathway is an extrapolation artifact rather than a physically faithful mechanism.
minor comments (2)
  1. [Methods] The training database is described at a high level ('diversified database of over 9000 configurations'); more detail on the distribution of high-temperature states and how extrapolation risk was quantified for the 8000-atom runs would strengthen the methods.
  2. [Results] Error bars or uncertainty estimates on the PDF comparisons and on the reported ring statistics during annealing are not mentioned; adding these would improve clarity of the validation.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the detailed and constructive review of our manuscript. We address the major comment regarding validation of the dynamical pathway below, and we outline revisions that will strengthen the presentation of our results.

read point-by-point responses

  1. Referee: [MD simulation results and validation section] The load-bearing claim is that the ML potential correctly drives carbon nucleation and the 5-/7- to 6-membered ring conversion during high-T annealing. However, validation is reported only via reproduction of experimental PDFs for the final structures (Abstract and results on MD trajectories). PDF agreement constrains equilibrium pair correlations but does not test relative energies or barriers of the defective-ring intermediates identified as mediating the transformation, leaving open the possibility that the observed pathway is an extrapolation artifact rather than a physically faithful mechanism.

    Authors: We agree that reproduction of experimental PDFs validates the final atomic configurations but does not directly probe the relative energies or barriers associated with the 5-/7- to 6-membered ring rearrangements. Our ML potential was trained on a diversified database of over 9000 configurations that explicitly includes high-temperature amorphous states, surfaces, and crystal structures, which encompass a broad range of carbon ring environments and defective motifs. This training strategy is intended to ensure faithful description of the relevant energetics. Nevertheless, to directly address the concern about possible extrapolation artifacts, the revised manuscript will include new analysis: we will report relative energies (computed with both the ML potential and reference DFT) for representative small-model systems containing 5-, 6-, and 7-membered carbon rings and their interconversions. These additional checks will confirm that the observed mediation pathway is consistent with the underlying potential energy surface learned from the training data. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation relies on external training data and experimental validation

full rationale

The paper trains a machine learning interatomic potential on an external diversified database of over 9000 configurations (including amorphous models and high-temperature states) and then performs large-scale MD simulations on 8000-atom systems. The reported phase separation and ring rearrangements emerge as simulation outcomes, with final structures validated against independent experimental PDFs. No equations, fitted parameters, or self-citations reduce the central claim to the inputs by construction; the workflow remains self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The central claim rests on the assumption that the ML potential trained on the stated database accurately captures high-temperature dynamics and that the observed phase separation is not an artifact of training-data selection or model limitations.

free parameters (1)
  • ML interatomic potential hyperparameters
    Neural-network weights and architecture choices fitted during training on the 9000-configuration database.
axioms (1)
  • domain assumption The diversified training database of over 9000 configurations sufficiently samples the relevant configuration space for amorphous, high-temperature, and surface states in Si-C-N-H systems.
    Invoked to justify that the potential can be applied to large-scale thermal-processing simulations without major extrapolation errors.

pith-pipeline@v0.9.0 · 5811 in / 1453 out tokens · 43339 ms · 2026-05-21T07:24:40.496184+00:00 · methodology

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