skip termini mods if none atoms are different

polyply/src/molecule_utils.py

@@ -286,6 +286,10 @@ def find_termini_mods(meta_molecule, molecule, force_field):
             for attr in ['atype', 'mass']:
                 if target_attrs[attr] != ref_attrs[attr]:
                     replace_dict[node][attr] = target_attrs[attr]
+        # a little dangerous but mostly ok; if there are no changes to
+        # the atoms we can continue
+        if len(replace_dict) == 0:
+            continue
 
         # bonded interactions could be different too so we need to check them
         overwrite_inters = defaultdict(list)