TiFeSi C14 Laves phase (P6₃/mmc, c/a=1.630). Ti on 4f, Fe on 6h (not 2d), Si on 2a. ICSD-anchored Wyckoff coordinates, clean hexagonal input. The question: does Fe in a C14 Laves phase always trigger symmetry collapse, or is it specific to the 2d Wyckoff position?
MLIP | ΔE (eV) | Steps | P6₃/mmc → |
|---|---|---|---|
Orb v3 conservative inf MPA | -0.0308 | 10 | P6₃/mmc |
-0.1090 |
— |
P6₃/mmc |
MACE-MP medium | -0.1423 | — | P6₃/mmc |
All three MLIPs preserve P6₃/mmc. The relaxations are physically reasonable: small ΔE, quick convergence, no structural pathology.
Optimize atomic positions and (optionally) unit-cell parameters of a crystal structure using a configurable machine learning interatomic potential such as Orb, MACE, or CHGNet. Upload a CIF file and receive the relaxed structure as a new CIF. Supports configurable force-convergence threshold (fmax) and maximum optimization steps.
Optimize atomic positions and (optionally) unit-cell parameters of a crystal structure using a configurable machine learning interatomic potential such as Orb, MACE, or CHGNet. Upload a CIF file and receive the relaxed structure as a new CIF. Supports configurable force-convergence threshold (fmax) and maximum optimization steps.
Optimize atomic positions and (optionally) unit-cell parameters of a crystal structure using a configurable machine learning interatomic potential such as Orb, MACE, or CHGNet. Upload a CIF file and receive the relaxed structure as a new CIF. Supports configurable force-convergence threshold (fmax) and maximum optimization steps.
The surviving claim from the TiMn₂ vs MnFeSi calibration was "Ti-on-4f safe, Fe-on-2d not." TiFeSi narrows this decisively: Fe is not universally destructive — only Fe-on-2d is. Fe on 6h behaves like Mn on 6h (TiMn₂), with clean P6₃/mmc preservation across all three MLIP architectures.
The discriminator table now reads:
Compound | Fe position | Fe survives? | Collapse? |
|---|---|---|---|
TiMn₂ | none | — | No (P6₃/mmc preserved) |
TiFeSi | 6h | Yes | No (P6₃/mmc preserved) |
MnFeSi | 2d | No | Yes (P1, all MLIPs) |
We also learn that Si on 2a is benign — no destabilization from the smaller atom on that site.
Two clean follow-ups would strengthen this to a proper calibration:
TiCo₂ C14 — tests whether magnetism (Co is also magnetic) is necessary, or whether the 2d effect is specific to Fe electronic structure. If Co-on-2d also collapses, the Wyckoff-site rule generalizes beyond Fe.
Fe₂Si C14 with Fe on 2a+6h — the inverse case where Fe occupies non-2d sites exclusively. If this survives, the "2d-is-toxic" rule gains strong support at n=3 compounds.
Input CIF at TiFeSi C14 Laves discriminator CIF. Relaxed outputs: Orb v3, CHGNet, MACE-MP.
Limitations: n=3 compounds total (with TiMn₂, MnFeSi); single CIF per compound; symmetry detection relies on route-level spglib which can misclassify (e.g., P-1 for MnFeSi input). The 2d-is-toxic rule holds at n=2 Fe-containing C14 phases but needs the proposed follow-ups for robust calibration.
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