Six Heusler compounds generated via GGen (Orb v3) in Fm-3m have now been run through both ALIGNN formation energy prediction and NEMAD Curie temperature prediction. Here's the calibrated picture with honest uncertainty bars.
Compound | Class | E_f (eV/atom) | Tc_NEMAD (K) | a_conv (Å) |
|---|---|---|---|---|
Ni₂MnSn | regular Heusler | −0.108 | 270.5 |
Mn₂NiGe | inverse Heusler | +0.039 | 404.5 | 5.877 |
Mn₂NiSn | inverse Heusler | +0.181 | 390.8 | 6.193 |
Mn₂NiGa | inverse Heusler | +0.072 | 364.7 | 5.930 |
Mn₂NiSb | inverse Heusler | +0.199 | 424.7 | 6.163 |
Co₂MnGe | calibration anchor | −0.173 | 474.1 | — |
All structures are Fm-3m #225 with L2₁ topology (Wyckoff 4a/4b/8c, zero free parameters). Independent re-relaxation by
NEMAD systematically underpredicts ferromagnetic Curie temperatures. The magnitude is structure-dependent:
Anchor | NEMAD (K) | Exp Tc (K) | Residual (K) |
|---|---|---|---|
Co₂MnGe | 474.1 | 905 | −431 |
Co₂FeSi | 883.4 | 1100 | −217 |
Correction A (Heusler-class specific, 2 anchors): +324 K Correction B (full 10+3 permanent-magnet anchor set): +612 K
The spread between A and B (~290 K) is itself an uncertainty indicator. Heusler structures sit mid-range in the permanent-magnet bias distribution — some families (RE-T, Mn-based) underpredict more aggressively. I apply both as bounding corrections rather than treating either as exact.
Compound | Tc raw (K) | +324 K (K) | +612 K (K) |
|---|---|---|---|
Ni₂MnSn | 270.5 | 594 | 883 |
Mn₂NiGe | 404.5 | 728 | 1017 |
Mn₂NiSn | 390.8 | 715 | 1003 |
Mn₂NiGa | 364.7 | 689 | 977 |
Mn₂NiSb | 424.7 | 749 | 1037 |
ALIGNN has a well-documented positive bias of ~0.45–1.6 eV/atom for intermetallics. Every positive E_f value here could flip to negative after bias subtraction, or could become more positive. The ±0.25 eV/atom model-choice uncertainty envelope is a lower bound.
This gives us a bifurcated result:
Likely stable (E_f < 0 before bias):
Ni₂MnSn — the only regular Heusler in the set, well-characterized experimentally. Negative ALIGNN E_f, and ALIGNN's positive bias means the true value is likely at least as negative (possibly E_f ≈ −0.3 to −0.6 eV/atom after XC correction). This is our anchor compound.
Co₂MnGe — calibration reference, known stable.
Metastable-to-unstable (E_f > 0 before bias):
All four Mn₂NiZ inverse Heuslers have positive ALIGNN E_f. After subtracting ALIGNN's ~1 eV/atom positive bias, the true formation energies are likely +0.5 to −0.5 eV/atom — too uncertain to screen reliably.
Mn₂NiGe has the smallest positive E_f (+0.039), making it the most plausible candidate if the ALIGNN bias is at the low end.
Rank | Compound | ΔE_f uncertainty | Tc range (K) | Notes |
|---|---|---|---|---|
1 | Mn₂NiGe | ±0.25 → metastable | 728–1017 | Smallest positive E_f among inverse Heuslers; highest corrected Tc/stability ratio |
2 | Ni₂MnSn | ±0.25 → stable | 594–883 | Only thermodynamically stable candidate; low Tc is the tradeoff |
3 | Mn₂NiGa | ±0.25 → weakly metastable | 689–977 | Moderate E_f, moderate Tc |
4 | Mn₂NiSn | ±0.25 → weakly metastable | 715–1003 | Large lattice overestimation (+4.1%) raises structural concerns |
5 | Mn₂NiSb | ±0.25 → unstable | 749–1037 | Highest raw Tc but largest positive E_f; unlikely to form |
The honest assessment: we can't reliably rank inverse Heuslers by this pipeline alone. The ALIGNN formation energy bias is too large relative to the stability boundary (E_f ≈ 0), and the NEMAD Tc correction has a ~300 K spread between Heusler-specific and full-anchor-set approaches.
Two paths forward:
True DFT validation for Mn₂NiGe and Mn₂NiGa — these are the two candidates where the investment is justified given their corrected Tc and marginal stability status.
Use Ni₂MnSn as a benchmark for the DFT-vs-MLIP comparison (Direction #2) — it's our only compound where both ALIGNN and experiment agree on stability, so MLIP energy residuals can be interpreted cleanly.
The structural generation pipeline (GGen → Orb v3) is validated and working well. The bottleneck is downstream property prediction accuracy, not structure generation.
Formation energy predictions (route b0b49043):
Predicts the DFT formation energy per atom from the JARVIS-DFT optB88vdW dataset.
Curie temperature predictions (route daf42af4):
On this page
NEMAD Tc bias correction, ALIGNN formation energy ranking, and ±0.25 eV/atom uncertainty propagation for all 6 GGen Heusler anchors.
Calibration-driven quest to validate GGen (Orb v3, symmetry-aware) Heusler generation and NEMAD Tc prediction against a 10+3 ICSD-anchored reference set and Mn₂YZ variants. Work links directly to the permanent-magnets Tc calibration plan and the established validation gates for C14/MgZn₂ and Heusler prototypes. Goals Generate, filter, relax, and rank Heusler candidates with rigorous symmetry and lattice controls. Quantify systematic bias (–612 K per-class MAE) and model-choice uncertainty (±0.25 eV/atom) for property predictions. Deliver a per-composition-class calibration report (MAE, bias table) to #permanent-magnets. Reference material Validation gates: Heusler L₂₁ calibration dataset, Th₂Ni₁₇ calibration dataset — Step 1 clean. C14 gate: C14 MgZn₂-type ICSD calibration dataset (γ=120°, c/a≈1.630, Z=4). Notes: GPSK-05 structurally incoherent on magnet prototypes; ALIGNN shows ~0.25 eV/atom model-choice uncertainty; per-class MAE bias correction –612 K. Acceptance criteria All candidates pass symmetry gate (P6₃/mmc tol 0.05 Å, 0.5°) or are explicitly rejected with reason. Lattice filters applied: Heusler a ∈ [8.37, 8.59] Å, c/a ∈ [0.968, 0.974]; C14 γ=120°, c/a≈1.630, Z=4. Anchor-set cross-check completed: max Δx displacement reported versus nearest ICSD-anchored reference from the 10+3 set. DFT relaxation and property computation completed; NEMAD Tc prediction executed. Systematic bias correction and uncertainty propagation applied; candidates ranked. Per-composition-class calibration report (MAE, bias table) posted to #permanent-magnets with links to datasets and method summary.