Re-add support for xTB

jitterbug/utils.py

@@ -32,5 +32,8 @@ def make_calculator(method: str, basis: Optional[str], **kwargs) -> Calculator:
         if not (basis is None or basis == "None"):
             raise ValueError(f'Basis must be none for method: {method}')
         return MOPAC(method=method, command='mopac PREFIX.mop > /dev/null')
+    elif method == 'xtb':
+        from xtb.ase.calculator import XTB
+        return XTB()
     else:
         return Psi4(method=method, basis=basis, **kwargs)

tests/test_utils.py

@@ -9,3 +9,5 @@ def test_make_calculator():
 
     with raises(ValueError):
         make_calculator('pm7', 'wrong')
+
+    assert make_calculator('xtb', None).name == 'xtb'