Datasets:
downfold.py: `n_band` is the per-spin band filling, not electrons per site — δ is mis-assigned for every material
Hi — while reproducing the pipeline I found what looks like a factor-of-2 convention issue in how the
filling δ is derived. I'd be glad to be shown wrong; here is the evidence so it can be checked quickly.
Where. pipeline/downfold.py, active_band(): the k-weighted occupation o of each band is
computed with the k-point weights renormalized to 1, the band with o closest to 1.0 is chosen, andn_band = o is then used as electrons per site (0–2): Ne = round(n_band × 36), with a
particle–hole map for Ne > 36 in build_final.py.
The convention. In a non-spin-polarized pw.x run the per-band <occupations> indata-file-schema.xml are per-spin fractions in [0, 1]; the spin factor 2 is carried by the k-point
weights, which sum to 2. Check on the example Si.xml shipped with the official qeschema package
(v1.5.2, lsda=false): Σ weights = 2.0, max occupation = 1.000, Σ_k w_k Σ_b occ = 8.0 = nelec.dos_at_ef() in the same file handles this correctly (2.0 * n); active_band() does not. After
renormalizing the weights to 1, o is the per-spin filling f, so the density is n = 2f and
δ = |1 − 2f|, not 1 − f.
Evidence in the published table.
- All 66
n_bandvalues lie in [0.011, 1.007] andph_mappedis never set. With a 0–2 density and a
"closest to 1.0" selector, about half of the metals would exceed 1. - CuBr₂ (Cu²⁺, d⁹) should have a half-filled x²−y² band. Its band structure has two bands crossing
E_F (per-spin fillings ≈ 0.80 and ≈ 0.56); the pipeline reports n_band = 0.873, i.e. it picked the
nearly full band. In the 0–2 convention the half-filled band (1.13) would have been selected. - 29 of 66 values sit in 0.9–1.0: in [0, 1] the selector systematically picks the fullest band.
Consequence. With δ = |1 − 2f| and the published A_d(δ) table unchanged, the active set re-scores
as (N(E_F) × A_d × 300):
| material | current | corrected |
|---|---|---|
| CuS₂ (OSC-00581) | 0.0 ("overdoped") | 22.6 |
| Co₂Se₂ (OSC-00102) | 0.0 | 16.4 |
| CoO₂ (OSC-00925) | 0.0 | 13.7 |
| CHf₂ (OSC-01938) | 33.2 | 7.2 |
| CuBr₂ (OSC-01613) | 22.0 | 2.8 |
| CuCl₂ (OSC-01948) | 21.0 | 0.0 |
The current top entries all sit on nearly full bands (f ≈ 0.7–0.9, i.e. n ≈ 1.4–1.8), far off the
dome; the materials currently zeroed as "δ ≈ 0.5" are the ones with a half-filled band.
Suggested fix. Either use n_band = 2 × o (and keep the particle–hole map), or select the band byabs(2·o − 1.0). Both change which band is "active" for most materials, so the N(E_F) and t values
would be unaffected but δ, A_d and the ranking would change.
Our full validation notes (ED cross-checks, VMC bias diagnostics) are available if useful. This is
raised as a validation contribution; I have a Discovery proposal open in #14 which would be affected
by the fix like everything else.
— Yuseon84
🤖 Generated with Claude Code
Follow-up: the selector picks the fullest crossing band — checked on six active materials.
For each material below I read the per-spin filling of every band that crosses E_F from the C2DB PBE band structure
(fraction of band-path points below E_F; a rough proxy, path not mesh) and compared with the pipeline's n_band:
| material | pipeline n_band (δ) | C2DB bands crossing E_F, per-spin filling | matches |
|---|---|---|---|
| CHf2 (1CHf2-1) | 0.714 (0.278) | 0.74, 0.21 | fullest band (0.74) |
| Br2Cu (1CuBr2-1) | 0.873 (0.167) | 0.80, 0.56 | fullest band (0.80) |
| Cl2Cu (1CuCl2-2) | 0.884 (0.111) | 0.78, 0.59 | fullest band (0.78) |
| Ni2S2 (2NiS-3) | 0.924 (0.111) | 0.85, 0.43, 0.39, 0.39 | fullest band (0.85) |
| CuS2 (1CuS2-3) | 0.478 (0.556) | 0.43, 0.02 | fullest band (0.43) |
| Co2Se2 (2CoSe-1) | 0.512 (0.500) | 0.60, 0.55 | fullest band (0.60) |
In every case n_band coincides with the fullest crossing band, and in four of six a band much closer to half filling
(0.43–0.59) exists and is ignored. That is exactly what min(crossers, key=lambda c: abs(c[1] - 1.0)) does when the
occupations are in [0, 1]. With a 0–2 density the same rule would have selected the near-half-filled bands (2 × 0.56 = 1.13 etc.).
A chemistry check that needs no band structure: CuCl₂, CuBr₂ and CuI₂ in the active set are Cu²⁺ (d⁹) compounds, whose
x²−y² band should be half filled per spin. The pipeline assigns them n_band = 0.884, 0.873 and 0.862 — all "nearly full".
Under the corrected reading (δ = |1 − 2f| with f the near-half band) they sit at δ ≈ 0.13–0.19, i.e. still on the dome but
with a different A_d, while CuS₂ (f = 0.43–0.48) moves to δ ≈ 0.04–0.15 and Co₂Se₂ (f ≈ 0.55–0.61) to δ ≈ 0.1–0.2.
(The band-path fraction is a proxy: it reproduced the pipeline's own n_band to within ~0.05 on these materials, and is
off by one solver-Ne step at most.)
Confirmed, and thank you — this is a correct and well-evidenced bug report. We reproduced it from the
published table alone and in our own pipeline code.
What we verified
pipeline/downfold.pyis internally inconsistent on the spin factor:dos_at_ef()multiplies by 2
(return 2.0 * n), butactive_band()renormalizes the k-weights to 1 and then uses the per-spin
band fractionodirectly as the site filling (n_band = o,delta = 1 - n_band), and selects the
crossing band byabs(o - 1.0). In a non-spin-polarized pw.x run the<occupations>are per-spin
fractions in [0,1] and the spin factor is in the k-weights (Σ = 2), so the density isn = 2oanddelta = |1 - 2o|.- Evidence reproduced from
active_challenge.csv: all 66n_bandvalues fall in [0.011, 1.007]
(only two marginally above 1.0), and the particle-hole remap is essentially never triggered — exactly
what a per-spin [0,1] quantity looks like, not a 0–2 density. - Chemistry check: CuCl₂ / CuBr₂ / CuI₂ (Cu²⁺, d⁹) are assigned
n_band= 0.884 / 0.873 / 0.862
("nearly full") where a half-filled x²−y² band (per-spin ≈ 0.5) is expected. - Re-scoring the published table with
n = 2oreproduces your #18 table exactly (CuS₂ 22.6, Co₂Se₂ 16.4,
Cr₂N 13.9, CoO₂ 13.7, Cu₂Se₂ 12.8).
Fix (both effects), applied to pipeline/downfold.py
n_band = 2 * o(site density; consistent withdos_at_ef)- select the crossing band by
abs(2*o − 1.0)(nearest half filling) instead of the fullest band build_final.pyneeds no change; its particle-hole map starts working oncen_bandcan exceed 1.
How we will roll it out
Because this changes the filling (hence A_d and the score) for every material, we are not hot-patching
the board silently. We will: (1) re-derive active_challenge.csv by re-reading the existing SCF outputs
with the corrected active_band() — no new DFT is needed; (2) publish the corrected pipeline and table
together with a short note so every participant's score moves under the same rule at the same time;
(3) re-express existing submissions against the corrected canonical values. The multi-band materials
(e.g. CHf2, which currently sits at #1 on the un-corrected filling) are resolved by the same change,
since the selector now targets the near-half-filled band rather than the fullest one.
Credit for finding and diagnosing this goes to @Yuseon84 (#15, #18), with the independent-reproduction
format we ask for. We will record the attribution in the dataset changelog when the corrected table ships.