# Crystal Bond Length Benchmark — v1-v10 (351 truly novel materials)

Machine-readable artifacts: `crystal_bond_lengths_benchmark.json`, `crystal_bond_lengths_benchmark.csv`

## Summary

- Total materials: 351
- Mean MAPE: 1.926%
- Median MAPE: 1.359%
- Max absolute error: 14.302%
- Distinct elements covered: 79
- Distinct structure categories: 64

## Methodology

Cold-blind validation. Each row prediction computed without engine knowledge of the experimental value. Cohorts v1 through v10 were constructed sequentially, each targeting structure classes not yet validated in prior cohorts. Zero overlap between any holdout cohort and the in-sample master benchmark.

## Per-material results (first 30 shown; full list in CSV/JSON)

| Formula | Cohort | Category | Coord | Pair | Exp (pm) | Pred (pm) | Err (pm) | Err % |
|---|---|---|---|---|---|---|---|---|
| LaB6 | v1 | Hexaboride | 12 | La-B | 305.1 | 308.19 | 3.09 | +1.01% |
| CeB6 | v1 | Hexaboride | 12 | Ce-B | 303.5 | 301.83 | 1.67 | -0.55% |
| CaB6 | v1 | Hexaboride | 12 | Ca-B | 303.0 | 302.89 | 0.11 | -0.04% |
| SrB6 | v1 | Hexaboride | 12 | Sr-B | 315.2 | 313.15 | 2.05 | -0.65% |
| EuB6 | v1 | Hexaboride | 12 | Eu-B | 306.0 | 310.94 | 4.94 | +1.61% |
| TiNiSn | v1 | Half-Heusler | 4 | Ni-Sn | 257.4 | 260.68 | 3.28 | +1.27% |
| ZrNiSn | v1 | Half-Heusler | 4 | Ni-Sn | 263.4 | 260.68 | 2.72 | -1.03% |
| HfNiSn | v1 | Half-Heusler | 4 | Ni-Sn | 262.0 | 260.68 | 1.32 | -0.50% |
| Mg2Si | v1 | Antifluorite | 4 | Mg-Si | 274.0 | 273.8 | 0.2 | -0.07% |
| Mg2Ge | v1 | Antifluorite | 4 | Mg-Ge | 277.6 | 275.28 | 2.32 | -0.83% |
| Mg2Sn | v1 | Antifluorite | 4 | Mg-Sn | 293.4 | 290.82 | 2.58 | -0.88% |
| Ca3PN | v1 | Anti-Perovskite | 6 | Ca-N | 254.0 | 252.72 | 1.28 | -0.50% |
| Ca3SnO | v1 | Anti-Perovskite | 6 | Ca-O | 248.0 | 245.27 | 2.73 | -1.10% |
| Ba3SnO | v1 | Anti-Perovskite | 6 | Ba-O | 273.0 | 273.71 | 0.71 | +0.26% |
| Bi2Te3 | v1 | Tetradymite | 6 | Bi-Te | 308.5 | 313.58 | 5.08 | +1.65% |
| Sb2Te3 | v1 | Tetradymite | 6 | Sb-Te | 305.0 | 277.09 | 27.91 | -9.15% |
| LaNi5 | v1 | CaCu5-type | 6 | La-Ni | 287.0 | 286.74 | 0.26 | -0.09% |
| CaCu5 | v1 | CaCu5-type | 6 | Ca-Cu | 284.0 | 278.4 | 5.6 | -1.97% |
| LaFe4Sb12 | v1 | Filled-Skutterudite | 6 | Fe-Sb | 258.0 | 254.9 | 3.1 | -1.20% |
| CeFe4Sb12 | v1 | Filled-Skutterudite | 6 | Fe-Sb | 257.6 | 254.9 | 2.7 | -1.05% |
| YbFe4Sb12 | v1 | Filled-Skutterudite | 6 | Fe-Sb | 258.7 | 254.9 | 3.8 | -1.47% |
| Y2Ti2O7 | v1 | Pyrochlore | 6 | Ti-O | 196.2 | 196.68 | 0.48 | +0.24% |
| La2Zr2O7 | v1 | Pyrochlore | 6 | Zr-O | 213.0 | 211.73 | 1.27 | -0.59% |
| Y2Sn2O7 | v1 | Pyrochlore | 6 | Sn-O | 208.5 | 208.99 | 0.49 | +0.23% |
| Ti3SiC2 | v1 | MAX-phase | 6 | Ti-C | 217.0 | 216.94 | 0.06 | -0.03% |
| Ti2AlC | v1 | MAX-phase | 6 | Ti-C | 215.0 | 218.16 | 3.16 | +1.47% |
| Cu3N | v1 | Anti-ReO3 | 2 | Cu-N | 190.4 | 192.13 | 1.73 | +0.91% |
| CsPbBr3 | v2 | Halide-Perovskite | 6 | Pb-Br | 295.0 | 309.62 | 14.62 | +4.96% |
| CsPbI3 | v2 | Halide-Perovskite | 6 | Pb-I | 314.0 | 310.55 | 3.45 | -1.10% |
| CsSnBr3 | v2 | Halide-Perovskite | 6 | Sn-Br | 290.0 | 282.12 | 7.88 | -2.72% |

## Sources

All experimental bond lengths cited from primary X-ray crystallography literature (Wyckoff, Pauling File, IUCr, ICSD). See the `source` field in each row of the JSON/CSV export.