release oc20 slabs data (#1843)

We got some interest in this data, finally getting around to releasing
it. Resolves #1842

Author: mshuaibii

docs/catalysts/datasets/oc20_slabs.md

@@ -0,0 +1,27 @@
+# Open Catalyst 2020 Surfaces Dataset
+
+:::{card} Dataset Overview
+
+| Property | Value |
+|----------|-------|
+| **Size** | 18.3M structures |
+| **Purpose** | Clean catalyst surfaces |
+| **Paper** | [UMA Paper](https://arxiv.org/pdf/2506.23971) |
+| **License** | [CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/legalcode) |
+:::
+
+## Overview
+
+This dataset contains the clean OC20 catalyst surfaces used to train UMA. Surfaces appearing in any OC20 test split were excluded to avoid data leakage. This filtering is strict — even surfaces in the in-domain test split are excluded to ensure fair S2EF evaluations.
+
+## File Contents and Download
+
+| Splits    | Size       | MD5 Checksum (Download Link) |
+|-----------|------------|------------------------------|
+| Train+Val | 18,323,074 | [f047cbd515f213d0b0925704abbb7ae5](https://dl.fbaipublicfiles.com/opencatalystproject/data/oc20/oc20_slabs.tar.gz) |
+
+The following metadata can be accessed in the `atoms.info` entry:
+
+- `sid`: Unique surface system identifier
+- `fid`: Frame index along the relaxation trajectory
+- `fmax`: Maximum per-atom force