GDML and Material definition for Thermal Scattering

Good morning Geant4 users,

I have a silly question for you. In order to correctly simulate thermal neutron scattering, it is necessary to create the elements that contain the information of neutron cross sections in the thermal energy range (e.g. TS_H_of_Water).

However, because of the complexity of the geometry of my model to be simulated I am using a GDML file. I know that GDML files can accept matrial assignment using NIST nomenclature (e.g. G4_H, etc.).

Unfortunately, when I try to use the nomenclature for thermal neutron scattering (having defined in my PhysicsList both the thermal data set and the model, as described in the example Hadr04) it gives me the error:
“Referenced material/element ‘TS_H_of_Water’ was not found”

Have any of you had the same problem? Do you know another way to call thermal data for a GDML file?

Thank you in advance for your help.