医学公开数据库查询与登记

references/cod.md

Base URL

https://www.crystallography.net/cod

Authentication

None required. COD is fully open-access with no API key needed.

Key Endpoints

Search by formula

GET /result?formula=Fe2%20O3&format=json

Formula format uses spaces between elements: Fe2 O3, Si O2, C6 H12 O6. URL-encode spaces as %20.

Search by elements

GET /result?el1=Fe&el2=O&format=json

Use el1, el2, el3, etc. for element filters. Use strictmin=2&strictmax=2 to restrict the number of distinct elements to exactly two. nel1, nel2, etc. exclude individual elements; they are not element counts.

Search by cell parameters

GET /result?amin=5.0&amax=6.0&bmin=5.0&bmax=6.0&cmin=5.0&cmax=6.0&format=json

Cell parameter filters:

• amin, amax — a-axis length (Angstroms)
• bmin, bmax — b-axis length
• cmin, cmax — c-axis length
• alpmin, alpmax — alpha angle (degrees)
• betmin, betmax — beta angle
• gamin, gamax — gamma angle
• vmin, vmax — unit cell volume (A^3)

Search by space group

GET /result?space_group_number=225&format=json

Search by text (author, journal, title)

GET /result?text1=perovskite&format=json

Combined search example

GET /result?el1=Ti&el2=O&strictmin=2&strictmax=2&space_group_number=136&format=json

Retrieve a specific CIF file

GET /1526463.cif

COD IDs are 7-digit integers. Append .cif for the crystallographic information file, or .html for the web page.

Retrieve entry metadata as JSON

GET /result?id=1526463&format=json

Output formats

• format=json — JSON array of matching entries
• format=csv — CSV output
• format=lst — list of COD IDs only
• Default (no format) — HTML page

Response Format

JSON is an array of entries; [] means no matching entry. The file string is the COD ID. Cell parameters and other numbers may also be strings, with unavailable fields null. The live 1526463 record (2026-09-30) has sgNumber="60", a="12.1005" and formula - Li2.78 O12 P3 V1.8 Zr0.2 -; it is not hematite. Fetch full structural data from https://www.crystallography.net/cod/{file}.cif.

Use the current search form's parameter names: unknown names can be ignored and yield an unintended broad query. Formula comparison follows COD's Hill-formatted formula conventions; validate the returned formula rather than treating element presence as exact stoichiometry.

Rate Limits

• No formal rate limits documented
• Be courteous: avoid bulk-downloading thousands of entries rapidly
• For bulk access, COD provides downloadable database dumps at https://www.crystallography.net/cod/archives/

Notes

• COD contains published crystal structures; record the retrieved entry revision for reproducibility.
• All data is open-access under public domain / open licenses
• The search API returns metadata; use the CIF endpoint for full structural data
• Alternative access: MySQL database dumps and SVN access are available for bulk use