updating 'rotconsts' ref to be compatible with cclib v1.8+

rmgpy/qm/molecule.py

@@ -409,18 +409,25 @@ def parse(self):
         parser.logger.setLevel(
             logging.ERROR
         )  # cf. http://cclib.sourceforge.net/wiki/index.php/Using_cclib#Additional_information
-        parser.rotcons = (
-            []
-        )  # give it an attribute and it won't delete it, leaving it on the parser object
+
         parser.molmass = None  # give it an attribute and it won't delete it, leaving it on the parser object
         cclib_data = parser.parse()
+
+        # for bacwards compatibility with cclib <1.6
+        if not hasattr(cclib_data, "rotconsts"):
+             # this hack required because rotconsts not part of a default cclib data object
+            parser.rotconsts = (
+                []
+            )  # give it an attribute and it won't delete it, leaving it on the parser object
+
+            cclib_data.rotconsts = (
+                parser.rotconsts
+            ) 
+
         radical_number = self.molecule.get_radical_count()
-        cclib_data.rotcons = (
-            parser.rotcons
-        )  # this hack required because rotcons not part of a default cclib data object
         cclib_data.molmass = (
             parser.molmass
-        )  # this hack required because rotcons not part of a default cclib data object
+        )  # this hack required because molmass is not part of a default cclib data object
         qm_data = parse_cclib_data(
             cclib_data, radical_number + 1
         )  # Should `radical_number+1` be `self.molecule.multiplicity` in the next line of code? It's the electronic ground state degeneracy.

rmgpy/qm/qmdata.py

@@ -98,7 +98,11 @@ def parse_cclib_data(cclib_data, ground_state_degeneracy):
             molecular_mass = None
         energy = (cclib_data.scfenergies[-1], 'eV/molecule')
         atomic_numbers = cclib_data.atomnos
-        rotational_constants = (cclib_data.rotcons[-1], 'cm^-1')
+        if hasattr(cclib_data, 'rotconsts'):
+            rotational_constants = (cclib_data.rotconsts[-1], 'cm^-1')
+        else:
+            rotational_constants = (cclib_data.rotcons[-1], 'cm^-1')
+
         atom_coords = (cclib_data.atomcoords[-1], 'angstrom')
         frequencies = (cclib_data.vibfreqs, 'cm^-1')