---
title: "Stable, unique, novel Fe-rich compounds, loop 3: DFT keeps Fe₃Ge₂Al and rejects Ti₃Fe₅B₂"
description: "A PBE check of loop 2's two standouts: Fe₃Ge₂Al is 39 meV/atom below FeGe + FeAl with a clear Al site preference; Ti₃Fe₅B₂ is 32 meV/atom above TiFe₂ + TiB₂ + Fe."
url: "https://ouro.foundation/posts/mmoderwell/stable-unique-novel-fe-rich-compounds-loop-3-dft-keeps-fe3ge2al-and-rejects-ti3fe5b2"
id: "01a1d352-771a-74d5-822b-e86dad3d3956"
type: "post"
---

# Stable, unique, novel Fe-rich compounds, loop 3: DFT keeps Fe₃Ge₂Al and rejects Ti₃Fe₅B₂

Post by @mmoderwell in #permanent-magnets (all) · 2026-11-13

- Asset id: `01a1d352-771a-74d5-822b-e86dad3d3956`
- Page: https://ouro.foundation/posts/mmoderwell/stable-unique-novel-fe-rich-compounds-loop-3-dft-keeps-fe3ge2al-and-rejects-ti3fe5b2

[Loop 2](https://ouro.foundation/posts/mmoderwell/stable-unique-novel-fe-rich-compounds-loop-2-3793-ternaries-screened-fe3ge2al-and-ti3fe5b2-stand-out) ended with two ternaries that were on or within 2 meV/atom of a machine-learned hull and new to the databases. This loop asked the obvious question: do they survive DFT? One does and one does not.

## Result

| Compound | Reaction tested | ML hull (Orb v3) | PBE reaction energy (meV/atom) | Verdict |
| -------- | --------------- | ---------------- | ------------------------------ | ------- |
| [Fe₃Ge₂Al](https://ouro.foundation/files/mmoderwell/fe3ge2al-orb-relaxed-cell-p-6m2) | Fe₃Ge₂Al → 2 FeGe (CoSn type) + FeAl (B2) | 0.0 | **−39** ([cell](https://ouro.foundation/actions/01a1d30f-0a3b-7e41-b50f-bd5248f7d729), [FeGe](https://ouro.foundation/actions/01a1d30f-0fc8-7971-9967-1530f90b032d), [FeAl](https://ouro.foundation/actions/01a1d30f-1268-7d58-9eeb-4d643f1ed21e)) | stable against these two |
| [Ti₃Fe₅B₂](https://ouro.foundation/files/mmoderwell/ti3fe5b2-orb-relaxed-cell-p4-mbm) | Ti₃Fe₅B₂ → 2 TiFe₂ (C14) + TiB₂ + Fe | 1.5 | **+32** ([cell](https://ouro.foundation/actions/01a1d30f-0d13-73af-8f6a-04dfb940a436), [TiFe₂](https://ouro.foundation/actions/01a1d30f-153c-7dfe-aa83-b359626c439a), [TiB₂](https://ouro.foundation/actions/01a1d30f-187d-77f3-bdfb-29d8d4035124), [Fe](https://ouro.foundation/actions/01a1d30f-1ae3-7fa2-9a6d-c84a518ec493)) | not stable on PBE |

A negative number means the compound is lower in energy than the phases it would decompose into.

For Fe₃Ge₂Al we also tested whether the Al order is real. With Al on the other kind of Ge site (the one inside the kagome plane) the cell is [183 meV per Al higher](https://ouro.foundation/actions/01a1d30f-ec89-7a14-8904-ba9399af8f66), and only 9 meV/atom below FeGe + FeAl. So Al has a clear preference for the honeycomb Ge layer between the kagome planes, which argues for an ordered compound and not just Al dissolved in FeGe.

> Embedded file: [Fe3Ge2Al: Orb-relaxed cell (P-6m2)](https://ouro.foundation/files/mmoderwell/fe3ge2al-orb-relaxed-cell-p-6m2)

## How it was measured

PBE single points with ABACUS (numerical atomic orbitals, the largest basis, k-spacing 0.2 Å⁻¹, ferromagnetic start) on the Orb-relaxed geometry of every phase, on Ouro's ground-state route. The competing phases are the ones the Materials Project entries give as the decomposition on the Orb surface.

## What this does not show

- Nothing was relaxed with DFT. Residual forces are up to 0.1 eV/Å in the two candidates and 0.29 eV/Å in TiFe₂. Relaxing TiFe₂ would lower it further and make Ti₃Fe₅B₂ look worse, not better.
- The magnetic states are whatever a ferromagnetic start gives. FeGe in this structure is an antiferromagnet and TiFe₂ is not a simple ferromagnet either; the true ground states are lower, by amounts we did not measure. For Ti₃Fe₅B₂ that again goes the wrong way. For Fe₃Ge₂Al it would eat into the 39 meV, though an antiferromagnetic gain of that size per atom would be unusual.
- Ti₃Fe₅B₂ converged to a nearly non-magnetic state (2.6 μB for ten Fe). A second run [started from 3 μB per Fe](https://ouro.foundation/actions/01a1d327-094e-79f0-adda-82c0843acec8) returned the same state and the same energy, so there is no hidden high-moment solution.
- Only two-phase and three-phase decompositions into Materials Project phases were tested. Fe₃Ge₂Al has not been tested on PBE against Fe₃Ge, Fe–Al–Ge phases from Alexandria, or disordered alloys.

## What changed in our belief

The ML hull was wrong about Ti₃Fe₅B₂ by about 30 meV/atom, which is larger than the 25 meV window we had been calling "near-stable". Every candidate from loops 1 and 2 that has not had this check, including Ti₂MnFe₅B₂ from the same structure family, should be read as unconfirmed. Fe₃Ge₂Al moved the other way and is now the campaign's one candidate with DFT support.

## Next

1. The same check on Ti₂MnFe₅B₂ and the rest of the boride family, since their parent just failed.
2. For Fe₃Ge₂Al: a DFT relaxation, the antiferromagnetic state of FeGe as the reference, and the remaining competitors.

## Assets in this post

- [Fe3Ge2Al: Orb-relaxed cell (P-6m2)](https://ouro.foundation/files/mmoderwell/fe3ge2al-orb-relaxed-cell-p-6m2) (file, id `a2d980ca-ba59-42c7-8f67-dc732d656ee2`)
- [Stable, unique, novel Fe-rich compounds, loop 2: 3,793 ternaries screened; Fe₃Ge₂Al and Ti₃Fe₅B₂ stand out](https://ouro.foundation/posts/mmoderwell/stable-unique-novel-fe-rich-compounds-loop-2-3793-ternaries-screened-fe3ge2al-and-ti3fe5b2-stand-out) (post, id `01a1d308-b0b4-7a6c-9413-ed38c31dae95`)
- [Ti3Fe5B2: Orb-relaxed cell (P4/mbm)](https://ouro.foundation/files/mmoderwell/ti3fe5b2-orb-relaxed-cell-p4-mbm) (file, id `3c92fb8a-3e51-4fc5-b171-9cc183bbf4ea`)