Crystal structure search
One query across three open computational materials databases over the OPTIMADE API. Search by chemical system — the elements a structure may contain — or by reduced formula.
Results are fetched live from the databases when you search — nothing is cached here.
The databases behind the box
OQMD
The Open Quantum Materials Database — around a million DFT-calculated structures. The only one of the three that also returns formation energy, distance above the convex hull and band gap.
Materials Project
The best-known open computational materials database, covering inorganic compounds with calculated electronic and thermodynamic properties.
Open Materials Database
A curated OPTIMADE provider with fast, reliable responses — a good fallback when the larger mirrors are busy.
Availability varies. These are publicly funded research mirrors, not commercial APIs, and any of them can be slow or briefly offline. If the database you pick fails or returns nothing, the query is retried against another and the result header tells you which one answered.
What the columns mean
| Field | Meaning |
|---|---|
| ID | The provider's own identifier for the structure entry. |
| Formula | Reduced chemical formula of the unit cell. |
| Elements | Chemical species present in the structure. |
| Sites | Number of atomic sites in the unit cell — a rough proxy for structural complexity. |
| ΔHf (eV/atom) | DFT formation energy per atom. Negative means the compound is more stable than its constituent elements. OQMD only. |
| Hull (eV/atom) | Energy above the convex hull. Zero means the phase is predicted thermodynamically stable; small positive values are metastable. OQMD only. |
| Eg (eV) | Calculated band gap. Zero indicates a metal; DFT systematically underestimates gaps in semiconductors. OQMD only. |
How to search
By elements takes a comma-separated list — Ti, O — and with only these elements ticked it returns the Ti–O chemical system: structures built from those elements and nothing else. Untick it to include structures that merely contain them, which is how you find dopants and multi-component phases.
By reduced formula takes a formula in reduced form, such as O2Ti or NaCl. Providers normalise formulas differently, so if a formula search comes back empty, try the same chemistry as an element search instead.
Common questions
What is OPTIMADE?
OPTIMADE is a common REST API specification that lets one query run unchanged against many materials databases. It is why a single search box here can reach the Materials Project, OQMD and the Open Materials Database without a separate integration for each.
Why did a provider return nothing?
The public OPTIMADE mirrors are research infrastructure and go down or time out from time to time. The search falls back to another provider when the one you picked fails or comes back empty, and the results header names the database that actually answered.
Are these experimental measurements?
No. These are computed structures from density functional theory. They are excellent for checking that a phase exists, comparing relative stability and screening candidates — but they are not a substitute for measured property data on a real specimen.
Let the AI run the queries for you
The materials chat and selector call these same databases mid-answer, pull the numbers into their reasoning, and cite which one each figure came from.