> For the complete documentation index, see [llms.txt](https://doc.duaer.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://doc.duaer.com/getting-started/mpdd.md).

# MPDD in Duaer

In Duaer: Structures in the Material-Property-Descriptor Database by formula or elements, with space group, crystal system, density, and machine-learned formation energy. One successful search uses 1 credit.
## What you get

Duaer MPDD searches the Material-Property-Descriptor Database, millions of structures with symmetry, density, and a machine-learned (SIPFENN) formation energy for fast screening.

Pick Duaer Data → MPDD in the node creator, or open the [data market](/getting-started/data-market.md). Related: [Alexandria](/getting-started/alexandria.md), [Materials Project](/getting-started/materials-project.md).

## When to use it

- Screen many structures of a composition by predicted formation energy.
- Get space group and density for a formula.

## When not to use it

- DFT-computed stability. Use [Alexandria](/getting-started/alexandria.md).
- Experimental structures. Use [Crystal structures (COD)](/getting-started/cod.md).

## Search on the canvas

1. Open the node creator and pick Duaer Data → MPDD.
2. Fill Formula (such as Fe2O3) or Elements (such as Fe,O).
3. Limit defaults to 10, max 20. Execute.

A search uses 1 credit only when it returns rows. No rows, wrong input, or an upstream failure uses 0.

## Call the API

- GET https://api.duaer.com/v1/data/mpdd?formula=Fe2O3
- Authorization: Bearer <Duaer key>

The call skill below matches Copy skill in the Duaer data market, with parameters, examples, and result fields.

## Call skill

Same text as Copy skill.

```
---
name: duaer-mpdd
description: >-
  Duaer MPDD. Structures in the Material-Property-Descriptor Database by formula or elements, with space group, crystal system, density, and machine-learned formation energy.
  One successful search uses 1 Duaer credit.
---

# Duaer MPDD

Duaer MPDD searches the Material-Property-Descriptor Database, millions of structures with symmetry, density, and a machine-learned (SIPFENN) formation energy for fast screening.

## When to use

- Screen many structures of a composition by predicted formation energy.
- Get space group and density for a formula.

## When not to use

- DFT-computed stability. Use https://skills.duaer.com/alexandria.md.
- Experimental structures. Use https://skills.duaer.com/cod.md.

## Call

`GET https://api.duaer.com/v1/data/mpdd?formula=Fe2O3`

Header: `Authorization: Bearer <Duaer key>`

Use an account key or a model API key.

Get a Duaer key: https://skills.duaer.com/keys.md

## Parameters

Provide `formula` or `elements`.

- `formula` — Formula such as Fe2O3. Matches the reduced formula.
- `elements` — Optional. Materials that contain all of these, such as Fe,O.
- `limit` — Optional. Rows to return, from 1 to 20. Default 10.

## Examples

- `GET https://api.duaer.com/v1/data/mpdd?formula=Fe2O3` — iron oxide structures with symmetry and density.
- `GET https://api.duaer.com/v1/data/mpdd?elements=Mg,Al,O&limit=5` — magnesium aluminium oxides.

## Result

The response is `{ "items": [...] }`. Each item has `source`, `title`, `url`, and `summary`, plus:

- `structureId` — provider id.
- `formula`, `formulaCell`, `elements`, `sites` — reduced formula, cell formula, elements, and atoms in the cell.
- `spaceGroup`, `spaceGroupNumber`, `crystalSystem` — symmetry.
- `densityGcm3`, `volumeA3` — density in g/cm³ and cell volume in ų.
- `predictedFormationEnergyEvPerAtom` — machine-learned formation energy, not DFT.

Fields without a value are left out.

## Credits

A search that returns at least one row uses 1 credit.
An empty search, a search that finds nothing, or a failed search uses 0.
Wrong input returns 400 with a message and uses 0.
No remaining credits returns 402 and does not search.
A missing key returns 401.

## Related

- https://skills.duaer.com/alexandria.md — Duaer Alexandria
- https://skills.duaer.com/materials-project.md — Duaer Materials Project

```
## Questions

### How many credits does a MPDD search use in Duaer?

One credit when Duaer returns rows. A search with no rows or an error uses 0.

### How reliable is formation energy in Duaer MPDD?

Duaer MPDD formation energy comes from the SIPFENN machine-learning model. Use it for fast screening and confirm with a DFT source.

## Related

- [Alexandria in Duaer](https://doc.duaer.com/getting-started/alexandria.md)
- [Materials Project in Duaer](https://doc.duaer.com/getting-started/materials-project.md)