The author assigned chainId/auth_asym_id corresponding to this starting model.
This corresponds to the chainId/auth_asym_id of the experimental models in the
PDB or comparative models in the Model Archive or the starting models referenced
via a DOI. If starting models are included in IHM_STARTING_MODEL_COORD, then
this will be the same as _ihm_starting_model_details.asym_id.