add icsd_oxidation_states - the set of oxidation states that are obse…

…rved at least 10 times in ICSD using ICSD_BV_PARAMS as guide. This is due to both common_oxidation_states and all_oxidation_states either grossly underproducing or overproducing the oxidation state count. The ICSD oxidation states in this commit are more reasonable, although there are still some things I would hand-tune

pymatgen/core/periodic_table.py

@@ -512,6 +512,11 @@ def common_oxidation_states(self):
         """Tuple of all known oxidation states"""
         return tuple(self._data.get("Common oxidation states", list()))
 
+    @property
+    def icsd_oxidation_states(self):
+        """Tuple of all oxidation states with at least 10 instances in ICSD database"""
+        return tuple(self._data.get("ICSD oxidation states", list()))
+
     @property
     def full_electronic_structure(self):
         """

pymatgen/core/tests/test_periodic_table.py

@@ -104,6 +104,7 @@ def test_oxidation_states(self):
         el = Element.Fe
         self.assertEqual(el.oxidation_states, (-2, -1, 1, 2, 3, 4, 5, 6))
         self.assertEqual(el.common_oxidation_states, (2, 3))
+        self.assertEqual(el.icsd_oxidation_states, (1, 2, 3, 4))
 
     def test_deepcopy(self):
         el1 = Element.Fe