---
title: "Fe22B6W (mp-1224794) is in the wrong magnetic state in Materials Project"
description: "MP's GGA run for Fe22B6W is nearly non-magnetic. Spin-polarized DFT on MP's own geometry puts the ferromagnetic state 211 meV/atom lower, more than the 148 meV/atom that keeps it off the hull."
url: "https://ouro.foundation/posts/mmoderwell/fe22b6w-mp-1224794-is-in-the-wrong-magnetic-state-in-materials-project"
id: "01a0d507-9ea7-70ba-b302-574d482b2c23"
type: "post"
---

# Fe22B6W (mp-1224794) is in the wrong magnetic state in Materials Project

Post by @mmoderwell in #permanent-magnets (all) · 2026-09-24

- Asset id: `01a0d507-9ea7-70ba-b302-574d482b2c23`
- Page: https://ouro.foundation/posts/mmoderwell/fe22b6w-mp-1224794-is-in-the-wrong-magnetic-state-in-materials-project

While checking a B-Fe-W energy-above-hull run for a Fe12BW4 candidate, one reference entry stood out. Our phase diagram puts **Fe22B6W** ([mp-1224794](https://next-gen.materialsproject.org/materials/mp-1224794)) on the convex hull. Materials Project puts it **0.148 eV/atom above** the hull.

> Embedded file: [Fe12BW4 phase diagram 2](https://ouro.foundation/files/mmoderwell/fe12bw4-phase-diagram-2)

The diagram comes from [this run](https://ouro.foundation/actions/01a0d65b-6b5f-7dbb-9bd0-c8d8095fbf73) of the energy-above-hull route. The route doesn't reuse MP's DFT energies. It re-relaxes every MP reference with Orb v3 (conservative, inf, MPA) and builds the hull from Orb energies, so the disagreement is Orb versus MP's GGA calculation.

## The MP calculation is almost non-magnetic

Fe22B6W is the τ-phase Fe23B6 (Cr23C6-type, 29-atom primitive cell) with one Fe replaced by W. MP's own Fe23B6 entry is the natural comparison:

| Entry | Source | Formation energy (eV/atom) | E above hull (eV/atom) | Total moment (μB/cell) | Moment per Fe (μB) |
| ----- | ------ | -------------------------- | ---------------------- | ---------------------- | ------------------ |
| Fe23B6 ([mp-542758](https://next-gen.materialsproject.org/materials/mp-542758)) | MP, GGA | −0.169 | 0.022 | 57.7 | 2.51 |
| Fe22B6W ([mp-1224794](https://next-gen.materialsproject.org/materials/mp-1224794)) | MP, GGA | −0.049 | 0.148 | 0.70 | 0.03 |
| Fe22B6W | Orb v3, this diagram | −0.217 | 0 (on hull) | — | — |

Fe23B6 has the expected moment for an iron-rich boride. The W-substituted entry has almost none. Replacing one Fe in 23 with W can't plausibly wipe out magnetism across the whole cell, which suggested MP's run converged to a low-spin solution.

## Checking it with DFT

To test that directly, I ran the [Magnetic moments](https://ouro.foundation/routes/mmoderwell/magnetic-moments) route twice on **MP's own Fe22B6W structure** ([CIF](https://ouro.foundation/files/mmoderwell/fe22b6w-mp-1224794-mp-geometry), no re-relaxation) at identical settings: ABACUS LCAO, PBE, PseudoDojo NC pseudopotentials with DZP orbitals, `ecutwfc` 100 Ry, `kspacing` 0.3 Å⁻¹, 0.05 eV Gaussian smearing. One run was spin-polarized from a ferromagnetic seed (4 μB per Fe). The other was forced non-magnetic, which is close to the 0.03 μB/Fe state MP converged to.

**Ferromagnetic** (`nspin: collinear`):

> Embedded route: [Magnetic moments](https://ouro.foundation/routes/mmoderwell/magnetic-moments)

**Non-magnetic** (`nspin: non_spin`):

> Embedded route: [Magnetic moments](https://ouro.foundation/routes/mmoderwell/magnetic-moments)

| State | Total energy (eV/cell) | Total moment (μB/cell) | Fe moments (μB) |
| ----- | ---------------------- | ---------------------- | --------------- |
| Ferromagnetic | −77554.264 | 46.4 | 1.69–2.87, mean 2.24 |
| Non-magnetic | −77548.146 | 0 | 0 |

The ferromagnetic state is **6.12 eV per cell lower, or 211 meV/atom (278 meV per Fe)**. B carries a small antiparallel moment (−0.33 μB) and W carries −0.82 μB, as expected for an early 5d atom in an Fe host. The saturation magnetization at this geometry is about 1.8 T. The converged moments are in the [ferromagnetic magCIF](https://ouro.foundation/files/mmoderwell/fe22b6w-magnetic-moments).

That 211 meV/atom is larger than the 148 meV/atom separating MP's entry from the hull. Apply it to MP's number and Fe22B6W moves from 0.148 above the hull to roughly 0.06 eV/atom below it (formation energy about −0.26 eV/atom). That's consistent with Orb placing it on the hull.

## How firm is this

- **The direction is solid.** MP's Fe22B6W energy is for a nearly non-magnetic state that is far from the ground state. The conclusion that it belongs on or near the hull survives unless the magnetic energy is overestimated by more than 30%.
- **The exact magnitude isn't.** The spin-state energy difference comes from a different code, basis, and pseudopotentials than MP's VASP PAW calculation. Magnetic energies are broadly transferable between codes, but not to the meV. The honest statement is "on or somewhat below the hull," not "60 meV below."
- **Geometry favors the magnet further.** MP's geometry was relaxed in the low-spin state. A ferromagnetic relaxation would expand the cell (magnetovolume effect) and lower the energy further, so using MP's geometry is conservative.
- **The full fix** would be to recompute Fe22B6W, Fe23B6, and the relevant B-Fe-W references ferromagnetically at one consistent setting and rebuild the hull. That's worth doing if Fe22B6W becomes a candidate in its own right.

## Takeaway for hull screening

MP `energy_above_hull` values for magnetic compounds are only as good as the magnetic state each calculation converged to. A quick sanity check is to compare `total_magnetization` against a close structural analog. An Fe-rich entry with a near-zero moment is a red flag. Here it hid a phase that is probably thermodynamically stable behind a 148 meV/atom penalty, and an MLIP hull caught it.

## Assets in this post

- [Fe12BW4 phase diagram 2](https://ouro.foundation/files/mmoderwell/fe12bw4-phase-diagram-2) (file, id `f60da025-93ba-4ccc-8c28-b813c58a426a`)
- [Magnetic moments](https://ouro.foundation/routes/mmoderwell/magnetic-moments) (route, id `0a23817e-af47-485a-9c56-5f2df0178b80`)
- [Fe22B6W (mp-1224794, MP geometry)](https://ouro.foundation/files/mmoderwell/fe22b6w-mp-1224794-mp-geometry) (file, id `efd3d729-1fb3-43c0-b582-6e8143483350`)
- [Fe22B6W magnetic moments](https://ouro.foundation/files/mmoderwell/fe22b6w-magnetic-moments) (file, id `54a5239d-e278-48b1-982a-58300bea2b0a`)