Hi @KyuJung_Jun
The theoretical tag comes from the ICSD database. If any of the matching ICSD structures is tagged as experimental, then we tag our material as theoretical: False.
Right now, we don’t match to partial occupancy ICSD, although that is in the works. We also plan on adding more databases such as TCOD and PCOD, as well as the Pauling Files.
For ordered structures, we use the structure matcher on the final MP structure as well as the initial structures to determine if they match to an ICSD entry. This way, we capture any structures that might change significantly in DFT relaxation.
Yes, a structure with no icsd_ids should always be theoretical: False for now. In the future, that will change as we add more databases that we match to.