materials-project

Materials Project API

Search and retrieve computed materials data from the Materials Project database (v3 API). Covers 150k+ inorganic crystalline materials with DFT-computed properties.

Authentication

All requests require the X-API-KEY header set to your Materials Project API key. Store it in the MP_API_KEY environment variable.

export MP_API_KEY="your_api_key_here"

API Base URL

https://api.materialsproject.org/v3

Search by Chemical Formula

curl -s -H "X-API-KEY: $MP_API_KEY" \
  "https://api.materialsproject.org/v3/materials/summary/?formula=Fe2O3&_fields=material_id,formula_pretty,band_gap,formation_energy_per_atom,energy_above_hull,symmetry,density&_limit=10"

Lookup by Material ID

curl -s -H "X-API-KEY: $MP_API_KEY" \
  "https://api.materialsproject.org/v3/materials/summary/?material_ids=mp-149&_fields=material_id,formula_pretty,band_gap,formation_energy_per_atom,energy_above_hull,symmetry,density,structure"

Filter by Band Gap Range

curl -s -H "X-API-KEY: $MP_API_KEY" \
  "https://api.materialsproject.org/v3/materials/summary/?band_gap_min=1.0&band_gap_max=2.0&_fields=material_id,formula_pretty,band_gap,formation_energy_per_atom&_limit=20"

Filter by Thermodynamic Stability

Find materials on or near the convex hull (energy_above_hull close to 0 = stable):

curl -s -H "X-API-KEY: $MP_API_KEY" \
  "https://api.materialsproject.org/v3/materials/summary/?energy_above_hull_max=0.025&elements=Li,Fe,O&_fields=material_id,formula_pretty,energy_above_hull,formation_energy_per_atom&_limit=20"

Filter by Elements

Search for materials containing specific elements:

curl -s -H "X-API-KEY: $MP_API_KEY" \
  "https://api.materialsproject.org/v3/materials/summary/?elements=Si,Ge&_fields=material_id,formula_pretty,band_gap,density&_limit=15"

Key Properties

Property	Description	Unit
band_gap	Electronic band gap	eV
formation_energy_per_atom	Formation energy per atom from elements	eV/atom
energy_above_hull	Energy above convex hull (0 = stable)	eV/atom
symmetry	Space group and crystal system	-
density	Computed density	g/cm^3
volume	Unit cell volume	Angstrom^3
nsites	Number of sites in the unit cell	-

Parse Results with Python

curl -s -H "X-API-KEY: $MP_API_KEY" \
  "https://api.materialsproject.org/v3/materials/summary/?formula=TiO2&_fields=material_id,formula_pretty,band_gap,energy_above_hull,density&_limit=10" \
  | python3 -c "
import sys, json
data = json.load(sys.stdin)
for mat in data.get('data', []):
    mid = mat.get('material_id', 'N/A')
    formula = mat.get('formula_pretty', 'N/A')
    bg = mat.get('band_gap', 'N/A')
    ehull = mat.get('energy_above_hull', 'N/A')
    rho = mat.get('density', 'N/A')
    print(f'{mid:12s} {formula:10s} Eg={bg} eV  Ehull={ehull} eV/at  rho={rho} g/cm3')
"

Pagination

Use _limit and _skip for pagination:

# First page
curl -s -H "X-API-KEY: $MP_API_KEY" \
  "https://api.materialsproject.org/v3/materials/summary/?elements=Cu,Zn&_fields=material_id,formula_pretty&_limit=50&_skip=0"

# Second page
curl -s -H "X-API-KEY: $MP_API_KEY" \
  "https://api.materialsproject.org/v3/materials/summary/?elements=Cu,Zn&_fields=material_id,formula_pretty&_limit=50&_skip=50"

Common Query Patterns

• Solar cell absorbers: band_gap_min=1.0&band_gap_max=1.8&energy_above_hull_max=0.05
• Wide band gap semiconductors: band_gap_min=3.0&band_gap_max=6.0
• Metals: band_gap_max=0&is_metal=true
• Specific composition: chemsys=Li-Fe-P-O (all materials in that chemical system)

Best Practices

1. Always specify _fields to limit response size and speed up queries.
2. Use energy_above_hull_max=0.025 to filter for thermodynamically stable phases.
3. Check is_deprecated field to avoid outdated entries.
4. Use chemsys for phase diagram queries across a chemical system.
5. Rate limit: keep requests under 5 per second to avoid throttling.
6. For bulk downloads, use the mp-api Python client instead of REST calls.

Data Integrity Rule

NEVER fabricate database results from training data. Every protein ID, gene name, compound property, pathway ID, structure detail, and metadata MUST come from an actual API response in this conversation. If the API returns no results, errors, or partial data, report exactly what happened. Do not "fill in" missing data from memory or make up identifiers.