Materials Project
The Materials Project runs large batches of density functional theory calculations to predict properties such as stability, electronic structure, and elastic behaviour for hundreds of thousands of materials, including ones that have not yet been made in a lab.
You reach the data through a free API after registering for a key, which lets you pull structured records straight into your own pipeline rather than scraping pages.
It is published under CC BY 4.0, so you can use it commercially as long as you credit the project.
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