I want to freeze core orbitals of my molecule and I know ElectronicStructureProblem has the possibility (es_problem = ElectronicStructureProblem(driver=driver, q_molecule_transformers=FreezeCoreTransformer())). Then, when I run the code to calculate the ground state energy of my molecule (res = calc.solve(problem=es_problem)), it says that 'FreezeCoreTransformer' object is not iterable. Which is the way then to freeze core orbitals without using deprecated libraries of Qiskit? Thank you very much in advance!