Restore calculator attachement in _calc_forces

Author: harveydevereux

janus_core/calculations/phonons.py

@@ -1003,7 +1003,7 @@ def _calc_forces(self, struct: PhonopyAtoms) -> ndarray:
         ndarray
             Forces on the structure.
         """
-        return PhonopyAtomsAdaptor.get_atoms(struct).get_forces()
+        return PhonopyAtomsAdaptor.get_atoms(struct, self.calc).get_forces()
 
     def run(self) -> None:
         """Run phonon calculations."""