diff --git a/MolecularNodes/md.py b/MolecularNodes/md.py
index f3176f36..2563fb7c 100644
--- a/MolecularNodes/md.py
+++ b/MolecularNodes/md.py
@@ -167,6 +167,7 @@ def att_chain_id():
         chain_id = univ.atoms.chainIDs
         chain_id_unique = np.unique(chain_id)
         chain_id_num = np.array(list(map(lambda x: np.where(x == chain_id_unique)[0][0], chain_id)))
+        mol_object['chain_id_unique'] = chain_id_unique
         return chain_id_num
     
     # returns a numpy array of booleans for each atom, whether or not they are in that selection