From 21dc58bff188fbe122686280af5adcc1ce38a5f3 Mon Sep 17 00:00:00 2001
From: Jonathan Shimwell <drshimwell@gmail.com>
Date: Mon, 17 May 2021 17:50:08 +0100
Subject: [PATCH 1/2] changing element to element.title to catch lowercase
 entries

---
 openmc/material.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/openmc/material.py b/openmc/material.py
index 0d4fec808..eeac3e637 100644
--- a/openmc/material.py
+++ b/openmc/material.py
@@ -521,6 +521,8 @@ class Material(IDManagerMixin):
             if element is None:
                 msg = 'Element name "{}" not recognised'.format(el)
                 raise ValueError(msg)
+        else:
+            element = element.title()
 
         if self._macroscopic is not None:
             msg = 'Unable to add an Element to Material ID="{}" as a ' \

From 90ff8fcb4a312ed1bf2b2563f44b16b915a2f5e3 Mon Sep 17 00:00:00 2001
From: Jonathan Shimwell <drshimwell@gmail.com>
Date: Wed, 19 May 2021 13:31:45 +0100
Subject: [PATCH 2/2] added checks and tests for cases in add_element

---
 openmc/material.py                | 13 ++++++++++++-
 tests/unit_tests/test_material.py |  9 +++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/openmc/material.py b/openmc/material.py
index eeac3e637..c6a8e6f44 100644
--- a/openmc/material.py
+++ b/openmc/material.py
@@ -522,7 +522,18 @@ class Material(IDManagerMixin):
                 msg = 'Element name "{}" not recognised'.format(el)
                 raise ValueError(msg)
         else:
-            element = element.title()
+            if element[0].islower():
+                msg = 'Element name "{}" should start with an uppercase ' \
+                      'letter'.format(element)
+                raise ValueError(msg)
+            if len(element) == 2 and element[1].isupper():
+                msg = 'Element name "{}" should end with a lowercase ' \
+                      'letter'.format(element)
+                raise ValueError(msg)
+            # skips the first entry of ATOMIC_SYMBOL which is n for neutron
+            if element not in list(openmc.data.ATOMIC_SYMBOL.values())[1:]:
+                msg = 'Element name "{}" not recognised'.format(element)
+                raise ValueError(msg)
 
         if self._macroscopic is not None:
             msg = 'Unable to add an Element to Material ID="{}" as a ' \
diff --git a/tests/unit_tests/test_material.py b/tests/unit_tests/test_material.py
index ee8c54da9..02e53a28d 100644
--- a/tests/unit_tests/test_material.py
+++ b/tests/unit_tests/test_material.py
@@ -54,6 +54,15 @@ def test_elements():
         m.add_element('U', 1.0, enrichment=70.0, enrichment_target='U235')
     with pytest.raises(ValueError):
         m.add_element('He', 1.0, enrichment=17.0, enrichment_target='He6')
+    with pytest.raises(ValueError):
+        m.add_element('li', 1.0)  # should fail as 1st char is lowercase
+    with pytest.raises(ValueError):
+        m.add_element('LI', 1.0)  # should fail as 2nd char is uppercase
+    with pytest.raises(ValueError):
+        m.add_element('Xx', 1.0)  # should fail as Xx is not an element
+    with pytest.raises(ValueError):
+        m.add_element('n', 1.0)  # check to avoid n for neutron being accepted
+
 
 def test_elements_by_name():
     """Test adding elements by name"""