OpXRD

OpXRD lets you match an experimental X-ray powder diffraction pattern against a reference database to identify the crystalline phases in a sample. Reach for it when you have measured XRD data and need to name the solid forms present, or find reference patterns for a given element combination. Where PyWPEM simulates and refines patterns from a crystal structure, OpXRD searches known patterns — the two are complementary sides of phase identification. See the Materials & Crystals overview for where this fits.

OpXRD overview

OpXRD integrates the opXRD database of over 10,000 X-ray powder diffraction (XRPD) patterns into the .bloom* platform. Patterns are indexed with CrystalNN crystal fingerprints, enabling fast similarity searches for phase identification and materials characterization.

What is X-ray powder diffraction?

X-ray powder diffraction measures how X-rays scatter off a polycrystalline sample. The resulting pattern of peaks at specific angles (2-theta) is a fingerprint of the crystal structure. By comparing measured patterns against a reference database, you can identify the crystalline phases present in a sample.

How OpXRD works

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The database is hosted on a Modal persistent volume, pre-loaded from the opXRD Zenodo repository. This avoids Zenodo rate limits and provides consistent sub-second query performance.

Database contents

Supported operations

search_patterns

Filter the database by element composition, space group, chemical formula, or institution. Returns matching patterns with metadata.

similarity_search

Compare a query XRD pattern against the database using CrystalNN crystal fingerprints. Returns the most similar patterns ranked by cosine similarity. Configurable threshold filters out low-similarity matches.

compute_fingerprint

Generate a CrystalNN crystal fingerprint from a crystal structure (CIF content or a structure dict) — not from a raw diffraction pattern. Use the resulting fingerprint for downstream similarity comparisons or clustering.

get_pattern

Retrieve a specific pattern by its database ID, including full 2-theta/intensity data and all associated metadata.

list_institutions

Browse contributing institutions and their pattern counts. Useful for filtering searches to trusted sources.

compute_statistics

Aggregate statistics: total patterns, element distributions, space group coverage, and institution breakdown.

When to use OpXRD

Use OpXRD when:

• You have experimental XRD data and need to identify crystalline phases
• You want to find reference patterns for specific element combinations
• You need to compare your synthesized material's diffraction pattern against known structures
• You are building a materials characterization report

Use PyWPEM instead when:

• You need to simulate a diffraction pattern from a crystal structure (CIF file)
• You need Rietveld refinement of experimental data
• You need PDF (pair distribution function) analysis
• You need peak fitting or background subtraction

Limitations

• The database is a snapshot of opXRD. Newly published patterns may not be included until the next database update.
• CrystalNN fingerprints capture overall pattern shape but may not distinguish between polymorphs with subtle peak differences.
• Amorphous materials produce broad humps rather than sharp peaks and are not well-represented in the database.

Citations

Hollarek D, Schopmans H, Östreicher J, Teufel J, Cao B, Alwen A, et al. opXRD: Open Experimental Powder X-Ray Diffraction Database. Advanced Intelligent Discovery. 2026;2(2):e202500044. doi: 10.1002/aidi.202500044

Hollarek D, Friederich P. opXRD: Open Experimental Powder X-ray Diffraction Database (dataset). Zenodo. 2025. doi: 10.5281/zenodo.15298026

FAQ

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