Mp-23154 far away from matched icsd structures corresponds to the experimentally known ground-state of Br2. Unfortunately, the structure is completely distorted due to a known GGA error ( It might be good to add a warning here. Previous versions of the DB still had a structure close to the experimental minmum, this one not. One can also see the experimental structure in the corresponding ICSD entries: Search Results - Access Structures

Same is true for I2.

I am wondering if it would make sense to report a RMS to the experimental/starting point structure?