Improve unphysical (greater than 1) occupancy handling in CifParser and add missing site label if not check_occu

pymatgen/io/cif.py

@@ -323,9 +323,9 @@ def __init__(
         """
         Args:
             filename (PathLike): CIF file, gzipped or bzipped CIF files are fine too.
-            occupancy_tolerance (float): If total occupancy of a site is between 1 and occupancy_tolerance, the
-                occupancies will be scaled down to 1.
-            site_tolerance (float): This tolerance is used to determine if two sites are in the same position,
+            occupancy_tolerance (float): If total occupancy of a site is between
+                1 and occupancy_tolerance, it will be scaled down to 1.
+            site_tolerance (float): This tolerance is used to determine if two sites are at the same position,
                 in which case they will be combined to a single disordered site. Defaults to 1e-4.
             frac_tolerance (float): This tolerance is used to determine is a coordinate should be rounded to an ideal
                 value. e.g. 0.6667 is rounded to 2/3. This is desired if symmetry operations are going to be applied.
@@ -1027,11 +1027,11 @@ def get_matching_coord(
 
             # Get occupancy
             try:
-                occu = str2float(data["_atom_site_occupancy"][idx])
+                occu: float = str2float(data["_atom_site_occupancy"][idx])
             except (KeyError, ValueError):
                 occu = 1
 
-            # If check_occu is True or the occupancy is greater than 0, create comp_d
+            # If don't check_occu or the occupancy is greater than 0, create comp_dict
             if not check_occu or occu > 0:
                 # Create site coordinate
                 coord: Vector3D = (
@@ -1073,7 +1073,7 @@ def get_matching_coord(
 
         if any(occu > 1 for occu in _sum_occupancies):
             msg = (
-                f"Some occupancies ({_sum_occupancies}) sum to > 1! If they are within "
+                f"Some occupancies ({filter(lambda x: x<=1, _sum_occupancies)}) sum to > 1! If they are within "
                 "the occupancy_tolerance, they will be rescaled. "
                 f"The current occupancy_tolerance is set to: {self._occupancy_tolerance}"
             )
@@ -1149,7 +1149,10 @@ def get_matching_coord(
             all_species_noedit = all_species.copy()  # save copy before scaling in case of check_occu=False, used below
             for idx, species in enumerate(all_species):
                 total_occu = sum(species.values())
-                if 1 < total_occu <= self._occupancy_tolerance:
+                if check_occu and total_occu > self._occupancy_tolerance:
+                    raise ValueError(f"Occupancy {total_occu} exceeded tolerance.")
+
+                if total_occu > 1:
                     all_species[idx] = species / total_occu
 
         if all_species and len(all_species) == len(all_coords) and len(all_species) == len(all_magmoms):
@@ -1198,6 +1201,7 @@ def get_matching_coord(
                         all_coords[idx],
                         lattice,
                         properties=site_properties,
+                        label=all_labels[idx],
                         skip_checks=True,
                     )
 
@@ -1278,8 +1282,6 @@ def parse_structures(
                 "in the CIF file as is. If you want the primitive cell, please set primitive=True explicitly.",
                 UserWarning,
             )
-        if not check_occu:  # added in https://github.com/materialsproject/pymatgen/pull/2836
-            warnings.warn("Structures with unphysical site occupancies are not compatible with many pymatgen features.")
 
         if primitive and symmetrized:
             raise ValueError(

tests/io/test_cif.py

@@ -731,17 +731,28 @@ def test_empty(self):
         cb2 = CifBlock.from_str(str(cb))
         assert cb == cb2
 
-    def test_bad_cif(self):
+    def test_bad_occu(self):
         filepath = f"{TEST_FILES_DIR}/cif/bad_occu.cif"
         parser = CifParser(filepath)
         with pytest.raises(
-            ValueError, match="No structure parsed for section 1 in CIF.\nSpecies occupancies sum to more than 1!"
+            ValueError, match="No structure parsed for section 1 in CIF.\nOccupancy 1.556 exceeded tolerance."
         ):
             parser.parse_structures(on_error="raise")
         parser = CifParser(filepath, occupancy_tolerance=2)
         struct = parser.parse_structures()[0]
         assert struct[0].species["Al3+"] == approx(0.778)
 
+    def test_not_check_occu(self):
+        # Test large occupancy with check_occu turned off
+        with open(f"{TEST_FILES_DIR}/cif/site_type_symbol_test.cif") as cif_file:
+            cif_str = cif_file.read()
+        cif_str = cif_str.replace("Te    Te 1.0000", "Te_label    Te 10.0", 1)
+
+        structs = CifParser.from_str(cif_str).parse_structures(check_occu=False)
+
+        assert len(structs) > 0
+        assert set(structs[0].labels) == {"Te_label", "Ge"}
+
     def test_one_line_symm(self):
         cif_file = f"{TEST_FILES_DIR}/cif/OneLineSymmP1.cif"
         parser = CifParser(cif_file)