# Validation

## Validation Pipeline

Every entry in the Scandium Dataset passes through a deterministic validation
pipeline before entering its tier.

### Structural Validation

1. **Nsites ≥ 2**: Eliminates single-atom entries (no meaningful structure)
2. **Volume > 10 ų**: Eliminates entries with zero or implausible volume
3. **Min distance check**: Flags overlapping atoms (OQMD artifact detector)
4. **Space group computation**: spglib symmetry detection

### Property Validation

1. **Target presence**: At least 2 of 3 targets (FE, EaH, BG) must exist
2. **Physical range**: FE in [-5, +5] eV/atom, BG in [0, ~10] eV
3. **Stability check**: EaH < 0.1 eV/atom or null (for Gold tier)

### Quality Flags

Flags are generated by validators and ingested during scoring:

| Flag | Meaning |
|------|---------|
| `overlapping_atoms` | Min distance < 0.5 Å |
| `corrupted_structure` | Structure JSON unparseable |
| `extreme_*` | Property outside physical range |
| `heavy_element` | Contains elements with Z > 92 |
| `noble_gas` | Contains noble gas elements |
| `missing_spacegroup` | No space group computed |
| `bad_volume` | Volume missing or zero |
| `missing_EaH` | EaH not available (known for JARVIS) |

## Tier Gates

### Raw (Gate 0)
- Source and formula present
- Fallthrough for all entries

### Validated (Gates 1-4)
1. Valid structure (nsites ≥ 2, volume > 10)
2. At least 2 of 3 targets present
3. No critical quality flags
4. Quality score ≥ 70

### Gold (Gates 5-8)
5. Not a duplicate (no duplicate_group)
6. No label conflicts (no disagreement flags)
7. Stable or near-stable (EaH < 0.1 or null)
8. Complete metadata (space_group, density, elements)

### Strict Gold (Gates 9-11)
9. Provenance complete (source_id + checksum)
10. Quality score ≥ 80 (calibrated: 85.2% valid at this threshold)
11. No known defects (volume > 0, density > 0, space_group present)

## Verification Reports

See `reports/validation_reports/` for:
- Per-source validation results
- Per-family validation results
- Cross-source agreement verification