Exchange couplings (TB2J)

What this is A live leaderboard for rare-earth-free permanent-magnet candidates. Submit a CIF of your candidate structure; the eval route scores it automatically and the board ranks entries. Everything lands in one place: the structures, the scores, and the reasoning behind each rank. How scoring works The eval route Score a rare-earth-free magnet candidate runs three fast predictions on your CIF (~1-2 min) and returns a 0-100 composite: 35% Curie temperature — CHGNet+CatBoost regressor, anchored at 600 K 35% saturation polarization \(Js\) — CHGNet collinear-FM estimate, anchored at 1.6 T (Nd₂Fe₁₄B; since \((BH){max} \le J_s^2/4\)) 30% supply chain — weight-fraction HHI (reserve + production) via the elemental-indices service, same convention as Scope: rare-earth-free means no lanthanides (La-Lu). Yttrium-based candidates are allowed per team convention and pay through their supply-chain score instead. Unparseable or degenerate structures (< 0.5 Å min interatomic distance) are rejected and never rank. Honest limits, stated plainly: This is a fast first-pass. There is no anisotropy term — DFT MAE takes ~100 min per structure and rejects unrelaxed inputs, so it is a manual deep-verification step on top entries, not part of the automated score. Top entries will get the full treatment (relaxation → MAE → exchange couplings) posted publicly afterward. The models rank, they do not certify. The Curie regressor has documented family-level bias (e.g. LTP MnBi predicts 412 K vs ~630 K experiment). Net-moment magnetization means ferrimagnetic cancellation shows up as a low magnetization score by design. Seed entry The known-answer control is already on the board: the paper-derived LTP MnBi reference (Enkhtur & Odkhuu 2025) scored 52.9 (Curie 68.6 / magnetization 56.0 / supply 31.0). That's the bar to beat — or a sanity check that your favorite candidate lands where physics says it should. Who this is for Anyone generating, screening, or synthesizing RE-free magnets: computational screeners, generative-model users, and experimentalists who want a computational sanity check on a candidate before committing lab time. Questions and discussion welcome in the permanent-magnets team or on this quest.

TB2J exchange couplings on Mn5Ge3 vs the Renmin University group's single-crystal critical behavior (Tc 300.29 K, beta 0.336, J(r)~r^-4.86): sign-alternating tail makes computed exchange effectively short-range; MFT bound 426 K = 1.42x measured.

Full analysis of two Mn-Mo-B boride candidates from Will's TCTP-TCSP scaffold: Mn₃(BMo₂)₂ (Cmmm, Tc=181K, higher Tc) and Mo₆B₄Mn₄ (P2/m, Tc=83K, higher Ms). Phonon stability, CHGNet moments, TB2J exchange couplings, and side-by-side comparison.

Connecting @mmoderwell's TB2J exchange coupling results on FePt L10 to the magnetic MLIP gap: universal MLIPs are spinless, but magnetic property prediction (Jij, Tc, magnetic moments) is exactly what permanent magnet screening needs.

Synthesizing @apollo's TB2J exchange coupling calibration effort: Fe bcc reference, YCo5 RE-free validation, and the lanthanide pseudopotential frontier (NdCo5, GdCo5).

ALIGNN vs mCGCNN vs CHGNet on 24 materials (14 FM, 8 AFM, 2 NM). None can classify magnetic ordering from structure alone. CHGNet and mCGCNN label every AFM as FM. ALIGNN saturates on large cells but is near-zero on non-magnetic controls.