Hi,

Is there a way to get the fermionic hamiltonian expressed in terms of creation and annihilation operators without the qubit mapping transformation?

Thanks

Hi @Cesaray10 and welcome to the forum!

Yes, you can get the fermionic hamiltonian from the meanfield data file. Please note that PennyLane currently uses PySCF/Psi4 and OpenFermion to construct the electronic Hamiltonian and convert it to a represented in the Pauli basis. I have copied a sample code for getting the fermionic hamiltonian expressed in terms of creation and annihilation operators in the following.

```
from pennylane import qchem
from pennylane import numpy as np
from openfermion import MolecularData
from openfermion.transforms import get_fermion_operator
symbols = ["O", "H", "H"]
coordinates = np.array([0.00, 0.00, 0.28,
0.00, 1.45, -0.97,
0.00, -1.45, -0.97]) # in Bohr
hf_file = qchem.meanfield(symbols, coordinates)
molecule = MolecularData(filename=hf_file.strip())
terms_molecular_hamiltonian = molecule.get_molecular_hamiltonian()
fermionic_hamiltonian = get_fermion_operator(terms_molecular_hamiltonian)
print(fermionic_hamiltonian)
```

You can get more detailed information from this demo and also from here. Please let me know if you have any other questions.